Balanced control method and system for controllable energy consumption type flexible direct current converter valve submodules

Abstract

The invention relates to a balance control method and system for controllable energy consumption type flexible direct current converter valve submodules, and belongs to the technical field of submodule balance. Comprising the following steps: after the retention factors of all sub-modules of the flexible DC converter valve are determined, forming an input voltage group by the product of the capacitor voltage of each sub-module and the corresponding retention factor; if the bridge arm current of the converter valve is greater than 0, selecting sub-modules with a small product of the number of input sub-modules in the next control period of the bridge arm from the input voltage group to input; and if the bridge arm current is less than or equal to 0, selecting the sub-modules with a large product of the number of the input sub-modules from the input voltage group to input. The input voltage of the sub-module is determined according to the determined retention factor and the capacitance voltage of the corresponding sub-module, the input voltage of the input sub-module is determined according to the input voltage and the bridge arm current, and balance control of the sub-module is achieved.

Description

Technical Field

[0001] The present invention relates to a balanced control method and system for a controllable energy-consuming flexible direct current converter valve submodule, belonging to the technical field of submodule balancing. Background Art

[0002] In recent years, the offshore wind power industry has developed rapidly. With the increase in the installed capacity of wind farms, considering the transmission distance and transmission efficiency of wind farms, the mainstream offshore wind power transmission method adopts a flexible direct current transmission system based on voltage source converters. Power transmission generally adopts a point-to-point form of a flexible direct current system.

[0003] When a fault occurs in the receiving-end converter station or the receiving-end AC power grid, the power delivery capacity of the transmission system is severely limited, while the offshore wind farm continues to output power. The surplus power generated will continue to charge the capacitor of the flexible DC converter valve submodule, causing the DC bus voltage to rise rapidly to the system overvoltage protection level, seriously endangering system safety.

[0004] In order to make the processing of surplus power more direct and flexible, the controllable energy-dissipating flexible DC converter valve adds an energy dissipation branch in each submodule of the converter valve bridge arm based on the traditional modular multilevel converter (MMC). After an AC fault occurs at the transmitting and receiving end, during the fault ride-through period, if the submodule capacitor voltage rises to the set value, the energy dissipation power electronic switch is triggered to open to discharge the energy stored in the capacitor, reduce the capacitor voltage, and protect the converter valve equipment from overvoltage damage.

[0005] The system solution of replacing MMC+DC energy dissipation device with controllable energy dissipation flexible direct-current valve has become an economically feasible new technology, but there are still some technical difficulties that limit its engineering application. Among them, the energy balance problem between submodules of controllable energy dissipation flexible direct-current valve is a technical difficulty. During the operation of controllable energy dissipation flexible direct-current valve, in addition to ensuring the balance of submodule capacitor voltage, the energy absorption balance between submodules must also be ensured during fault crossing; otherwise, during fault crossing, it is very easy for the energy absorption branch between submodules to diverge, and batches of submodules will exit the available state of energy dissipation, causing the system to trip and break due to insufficient absorption of surplus energy.

[0006] The existing energy balancing strategy for controllable energy-consuming flexible direct-acting valve submodules requires sorting and balancing control from two dimensions: submodule voltage and absorbed energy. This has the following problems:

[0007] The bridge arm controller is required to calculate the amount of energy absorbed by each sub-module, which results in more valve control resources being occupied by the flexible direct-current valve, which is not conducive to project implementation.

[0008] The energy absorbed by each submodule is sorted. During the normal operation and voltage balancing of the submodules, additional submodules are switched on and off according to the energy absorption. This greatly increases the switching frequency of the submodules and the loss of the flexible DC converter valve. The high-frequency instructions generated seriously affect the reliable operation of the submodule power devices. Summary of the invention

[0009] The purpose of the present invention is to provide a balanced control method and system for controllable energy-consuming flexible direct current converter valve submodules, so as to solve the problem of increased losses of the flexible direct current converter valve caused by switching on and off additional submodules according to the energy absorption size.

[0010] To achieve the above object, the solution of the present invention includes:

[0011] A balanced control method of a controllable energy-consuming flexible direct current converter valve submodule of the present invention comprises the following steps:

[0012] After the holding factors of all submodules of the flexible DC converter valve are determined, the product of the capacitor voltage of each submodule and the corresponding holding factor constitutes an input voltage group;

[0013] If the bridge arm current of the converter valve is greater than 0, then select from the input voltage group: a submodule with a smaller product of the number of input submodules in the next control cycle of the bridge arm to be input;

[0014] If the bridge arm current is less than or equal to 0, then the submodule with the larger product of the number of submodules to be put into operation is selected from the input voltage group;

[0015] The retention factor of the normally functioning submodule among all submodules is determined as follows:

[0016] If the energy-discharging branch of the submodule is in an unavailable state, or the action number deviation of the energy-discharging branch in an available state is equal to 0, the holding factor of the submodule adopts a conventional holding factor slightly greater than 1;

[0017] If the deviation of the number of actions is greater than 0, the holding factor of the submodule adopts a positive bias holding factor that is smaller than the normal holding factor;

[0018] If the deviation of the number of actions is less than 0, the holding factor of the submodule adopts a negative bias holding factor that is greater than the normal holding factor.

[0019] Further, the small products are selected in the input voltage group in the order from small to large.

[0020] Further, the large products are selected in the order from large to small in the input voltage group.

[0021] Furthermore, the holding factor of the submodule that is not operating normally among all the submodules adopts the holding factor of the previous control cycle.

[0022] Furthermore, the calculation formula of the positive bias holding factor is as follows:

[0023] K Z =K a -ΔS sm *K b

[0024] In the formula, K Z is the positive bias holding factor, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is a value slightly larger than 0, sm is the number of the submodule, sm∈[1,N].

[0025] Furthermore, the calculation formula of the negative bias holding factor is as follows:

[0026] K F =K a -ΔS sm *K b

[0027] In the formula, K F is the negative bias holding factor, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is a value slightly larger than 0, sm is the number of the submodule, sm∈[1,N].

[0028] Furthermore, the calculation formula of the action number deviation is as follows:

[0029] ΔS sm =S sm -S ref

[0030]

[0031] In the formula, ΔS sm is the deviation of the number of actions, S sm is the number of times the energy-dissipating branch operates, S ref is the average number of actions of the energy-discharging branch in the available state, sm is the number of the submodule, sm∈[1,N], and m is the number of energy-discharging branches in the available state.

[0032] A balancing control system of a controllable energy-consuming flexible direct current converter valve submodule of the present invention comprises a processor, and the processor is used to execute a computer program to implement the steps of the balancing control method of the controllable energy-consuming flexible direct current converter valve submodule as described above.

[0033] Beneficial effects of the present invention:

[0034] The present invention is a pioneering invention, which provides a balanced control method for a controllable energy-consuming flexible direct current converter valve submodule, determines the input voltage of the submodule according to the determined submodule holding factor and the capacitor voltage of the corresponding submodule, and then determines the input voltage of the input submodule according to the input voltage of the submodule and the size of the converter valve bridge arm current, so as to realize the balanced control of the controllable energy-consuming flexible direct current converter valve submodule. Among them, the holding factor of the normal operation submodule is determined according to the state (available or unavailable) of the energy discharge branch of the converter valve submodule and the deviation of the number of actions of the energy discharge branch. The balancing method no longer increases the control variables for the submodule voltage balancing control, can be combined with the number of actions of each submodule energy discharge branch, and dynamically corrects the holding factor of each submodule through the deviation of the number of actions of the energy discharge branch, so that the energy absorption of the energy discharge branch between the submodules is balanced, and the complexity of the energy balance of the submodules is reduced, the amount of calculation is small, the implementation is simple, and the average switching frequency of the submodule is no longer increased, and the loss of the flexible direct current converter valve is effectively reduced, and the problem of uneven distribution of absorbed energy between submodules is solved, which is easy for engineering application. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a topological structure diagram of a controllable energy-consuming flexible straight valve;

[0036] Figure 2 It is a schematic diagram of the collection and control of control variables of the balanced control of the controllable energy-consuming flexible straight valve submodule;

[0037] Figure 3 It is a flow chart of a balanced control of a controllable energy-consuming flexible straight valve submodule;

[0038] Figure 4 This is a rendering of the average switching frequency of the submodule obtained by using the balanced control method of the controllable energy-consuming flexible straight valve submodule;

[0039] Figure 5 This is a diagram showing the effect of submodule energy balance obtained by using a balanced control method for a controllable energy-consuming flexible straight valve submodule;

[0040] Figure 6 It is a flow chart of another balanced control of the controllable energy-consuming flexible straight valve submodule. DETAILED DESCRIPTION

[0041] In order to solve the problem in the background technology, the present invention determines the input voltage of the submodule according to the determined submodule holding factor and the capacitor voltage of the corresponding submodule, and then determines the input voltage of the input submodule according to the input voltage of the submodule and the size of the bridge arm current of the converter valve, so as to realize the balanced control of the controllable energy-consuming flexible direct current converter valve submodule. Among them, the holding factor of the normally operating submodule is determined according to the state of the energy discharge branch (available or unavailable) and the deviation of the number of actions of the energy discharge branch. The balanced control method of the present invention no longer adds additional control variables for submodule voltage balancing control, and can combine the number of actions of each submodule energy discharge branch, and dynamically correct the holding factor of each submodule, so that the energy absorption of the energy discharge branch between the submodules is balanced, reducing the complexity of the energy balance of the submodule, with less calculation and simple implementation, without increasing the average switching frequency of the submodule, effectively reducing the loss of the flexible direct current converter valve, solving the problem of uneven distribution of absorbed energy between submodules, and being easy for engineering application.

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0043] An embodiment of a balanced control method for a controllable energy-consuming flexible direct current converter valve submodule:

[0044] A balanced control method for a controllable energy-consuming flexible direct current converter valve submodule comprises the following steps:

[0045] After the holding factors of all submodules of the flexible DC converter valve are determined, the product of the capacitor voltage of each submodule and the corresponding holding factor constitutes an input voltage group;

[0046] If the bridge arm current of the converter valve is greater than 0, then select from the input voltage group: a submodule with a smaller product of the number of input submodules in the next control cycle of the bridge arm to be input;

[0047] If the bridge arm current is less than or equal to 0, a submodule with a larger product of the number of submodules in the voltage group is selected for input.

[0048] Among them, the retention factor of the submodule that operates normally among all submodules is determined by the following method:

[0049] If the energy-discharging branch of the submodule is in an unavailable state, or the action number deviation of the energy-discharging branch in an available state is equal to 0, the holding factor of the submodule adopts a conventional holding factor slightly greater than 1;

[0050] If the deviation of the number of actions of the energy-discharging branch in the available state is greater than 0, the holding factor of the submodule adopts a positive bias holding factor that is less than the normal holding factor and greater than 0;

[0051] If the deviation of the number of actions of the energy-dissipating branch in the available state is less than 0, the holding factor of the submodule adopts a negative bias holding factor that is greater than the normal holding factor.

[0052] The available state means that the submodule and the energy dissipation branch are both fault-free at the current moment, and the energy absorbed by the energy dissipation resistor is less than the upper limit of its energy absorption. In this state, the energy dissipation branch can discharge energy at any time.

[0053] The unavailable state means that the submodule or the energy dissipation branch has a fault at the current moment, or the accumulated energy absorbed by the energy dissipation resistor reaches the upper limit of the energy absorption of the energy dissipation resistor. In this state, the energy dissipation resistor needs to be cooled and cannot perform the energy dissipation action.

[0054] Conventional retention factor K a ∈(1,2).

[0055] Specifically, the smaller product as the input voltage can be selected from the input voltage group in ascending order, or can be selected from the input voltage group according to a set threshold. Of course, other methods can also be used to select from the input voltage group.

[0056] Specifically, the larger one as the product of the input voltages can be selected from the input voltage group in descending order, or can be selected from the input voltage group according to a set threshold. Of course, other methods can also be used to select from the input voltage group.

[0057] Specifically, the calculation formula of the positive bias holding factor is as follows:

[0058] K Z =K a -ΔS sm *K b

[0059] In the formula, K Z is the positive bias holding factor, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is slightly greater than 0, K b ∈(0,1), sm is the number of the submodule, sm∈[1,N], K a ∈(1, 2), the value of the action number deviation ∈[1, N].

[0060] Specifically, K b ∈(0, 0.1].

[0061] Specifically, the calculation formula of the negative bias holding factor is as follows:

[0062] K F =K a -ΔS sm *Kb

[0063] In the formula, K F is a negative bias holding factor greater than 1, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is slightly greater than 0, K b ∈(0,1), sm is the number of the submodule, sm∈[1,N], K a ∈(1, 2), the value of the action number deviation ∈[1, N].

[0064] Specifically, K b ∈(0, 0.1].

[0065] Specifically, the calculation formula for the action number deviation is as follows:

[0066] ΔS sm =S sm -S ref

[0067]

[0068] In the formula, ΔS sm is the deviation of the number of actions, S sm is the number of times the energy-dissipating branch operates, S ref is the average number of actions of the energy-discharging branch in the available state, sm is the number of the submodule, sm∈[1,N], and m is the number of energy-discharging branches in the available state.

[0069] As another implementation, the action number deviation may also be set based on experience.

[0070] Specifically, the holding factor of the submodule that is not operating normally among all the submodules adopts the holding factor of the previous control cycle.

[0071] The retention factor of the previous control cycle is set according to the status of the submodule, system requirements and control strategy.

[0072] As another implementation, the retention factor of the submodule that is not operating normally among all the submodules may also be determined by an existing method.

[0073] As another implementation method, a balanced control method of a controllable energy-consuming flexible direct current converter valve submodule is as follows: Figure 3 As shown, the following steps are included:

[0074] 1) Obtain bridge arm control information and submodule status information.

[0075] The bridge arm control information includes the number of submodules n that will be put into operation in the next control cycle of the bridge arm. on(i.e., the number of submodules put into operation in the next control cycle of the aforementioned bridge arm) and the bridge arm current i arm ; The submodule status information includes the submodule voltage u of each submodule in the bridge arm sm (i.e. the capacitor voltage of the aforementioned submodule), the available state E of the energy dissipation branch of the submodule sm The number of times the energy dissipation branch of the sum module operates S sm (sm=1, 2, 3, …, N).

[0076] The submodule status information refers to the submodule status information of the submodule operating normally, because the status information cannot be seen for the submodule operating abnormally, and the faulty submodule in the abnormal operation has been bypassed and no longer participates in the control.

[0077] Among them, the available state of the submodule energy dissipation branch is E sm The energy dissipation branch including the submodule is in an unavailable state (i.e., E sm = 0) and the energy dissipation branch of the submodule is in an available state (i.e., E sm =1); that is: if E sm = 0, the energy dissipation branch of the submodule is considered to be unavailable; if E sm =1, it is considered that the energy dissipation branch of the submodule is in an available state.

[0078] Among them, Figure 2 As shown, the bridge arm control information is calculated by the upper valve control (converter valve controller), the submodule status information is calculated by the submodule controller, the bridge arm control information and the submodule control information are uniformly sent to the bridge arm controller, and the bridge arm controller performs submodule balancing control calculations.

[0079] 2) If the submodule is unavailable for energy dissipation (i.e., the energy dissipation branch of the submodule is in an unavailable state), or the energy dissipation branch of the available submodule has no deviation in the number of actions (i.e., the deviation of the number of actions of the energy dissipation branch in the available state is equal to 0), then the optimization strategy 1 is adopted, that is, the retention factor K of the submodule is sm1 Using the conventional holding factor K a (i.e. conventional retention factor), K sm1 =K a .

[0080] If the energy dissipation branch of the submodule is in an unavailable state (i.e., E sm =0), the balancing control strategy of the submodule remains unchanged, and the holding factor of the submodule adopts the conventional holding factor K a , K a is a value slightly greater than 1.

[0081] If the energy dissipation branch of the submodule is in an available state (i.e., E sm=1), calculate the average number of actions of the energy-discharging branch in the available state Then, the action times deviation ΔS of each energy-discharging branch in the available state is obtained. sm =S sm -S ref .

[0082] For the submodules whose energy-discharging branch is in an available state, according to the action times deviation ΔS of the energy-discharging branch sm Obtain the retention factor of the corresponding submodule. If ΔS sm =0, that is, the action times deviation is equal to 0, indicating that the energy absorbed by the energy dissipation branch of the submodule meets expectations, the submodule's balancing control strategy remains unchanged, and the submodule's holding factor adopts the conventional holding factor K a , K a is a value slightly greater than 1.

[0083] 3) If the energy dissipation branch of the submodule is in an available state (i.e. E sm =1), and the number of actions of the submodule energy dissipation branch is biased, that is, ΔS sm ≠0, use optimization strategy 2, that is, use a dynamically adjusted retention factor K according to the deviation size sm2 , K sm2 =K a -ΔS sm *K b .

[0084] Among them, if ΔS sm >0, that is, the deviation of the number of actions is greater than 0, and the number of actions of the energy-discharging branch is positively biased, indicating that the energy absorbed by the energy-discharging branch of the submodule is too large. According to the size of the positive bias of the number of actions of the energy-discharging branch, a holding factor K that is smaller than the conventional holding factor is used as the positive bias holding factor. a -ΔS sm *K b (K b is a value slightly greater than 0), that is, the holding factor of this submodule adopts a positive bias holding factor that is smaller than the conventional holding factor and greater than 0.

[0085] If ΔS sm <0, that is, the deviation of the number of actions is less than 0, and the number of actions of the energy-discharging branch is negatively biased, indicating that the energy absorbed by the energy-discharging branch of the submodule is too small. According to the magnitude of the negative bias of the number of actions of the energy-discharging branch, a holding factor K larger than the conventional holding factor is used as the negative bias holding factor. a -ΔS sm *K b (K b is a value slightly greater than 0), that is, the holding factor of this submodule adopts a negative bias holding factor that is greater than the conventional holding factor.

[0086] 4) Determine the submodule to be put into operation according to the size of the bridge arm current and the number of submodules put into operation, and use the holding factor method to sort the submodules and control the voltage balance.

[0087] After all the submodules of the converter valve are operating normally and the holding factors of all the normally operating submodules of the converter valve are determined, the holding factors of these submodules are multiplied by the corresponding submodule capacitor voltages to obtain the product as the input voltage, and the input voltages are sorted from low to high to obtain an input voltage group.

[0088] After all submodules of the converter valve are partially operating normally and the holding factors of all submodules of the converter valve are determined, the holding factors of these submodules are multiplied by the corresponding submodule capacitor voltages to obtain the product of the input voltages, and the input voltages are sorted from low to high to obtain an input voltage group.

[0089] The retention factor of the submodule that is not operating normally is determined using an existing method.

[0090] Alternatively, the holding factor of the submodule that is not operating normally adopts the holding factor of the previous control cycle.

[0091] The retention factor of the previous control cycle is set according to the status of the submodule, system requirements and control strategy.

[0092] If the bridge arm current i arm >0, input voltage n with lower input voltage in the input voltage group on sub-modules. If the bridge arm current i arm ≤0, input voltage higher n on submodules.

[0093] The number of submodules put into operation refers to the number of submodules put into operation in the next control cycle of the bridge arm n on .

[0094] As another implementation method, a balanced control method of a controllable energy-consuming flexible direct current converter valve submodule is as follows: Figure 6 As shown, the following steps are included:

[0095] Determine whether the submodule is running normally.

[0096] If the submodule is not operating normally, the balancing control strategy of the submodule remains unchanged, and the holding factor of the submodule adopts the holding factor of the previous control cycle.

[0097] The retention factor of the previous control cycle is set according to the status of the submodule, system requirements and control strategy.

[0098] If the submodule runs normally, perform the following steps:

[0099] 1) Obtain bridge arm control information and submodule status information.

[0100] The bridge arm control information includes the number of submodules n that will be put into operation in the next control cycle of the bridge arm. on (i.e., the number of submodules put into operation in the next control cycle of the aforementioned bridge arm) and the bridge arm current i arm ; The submodule status information includes the submodule voltage u of each submodule in the bridge arm sm (i.e. the capacitor voltage of the aforementioned submodule), the available state E of the energy dissipation branch of the submodule sm The number of times the energy dissipation branch of the sum module operates S sm (sm=1, 2, 3, …, N).

[0101] Among them, the available state of the submodule energy dissipation branch is E sm The energy dissipation branch including the submodule is in an unavailable state (i.e., E sm = 0) and the energy dissipation branch of the submodule is in an available state (i.e., E sm =1); that is: if E sm = 0, the energy dissipation branch of the submodule is considered to be unavailable; if E sm =1, it is considered that the energy dissipation branch of the submodule is in an available state.

[0102] Among them, Figure 2 As shown, the bridge arm control information is calculated by the upper valve control (converter valve controller), the submodule status information is calculated by the submodule controller, the bridge arm control information and the submodule control information are uniformly sent to the bridge arm controller, and the bridge arm controller performs submodule balancing control calculations.

[0103] 2) If the submodule is unavailable for energy dissipation (i.e., the energy dissipation branch of the submodule is in an unavailable state), or the energy dissipation branch of the available submodule has no deviation in the number of actions (i.e., the deviation of the number of actions of the energy dissipation branch in the available state is equal to 0), then the optimization strategy 1 is adopted, that is, the retention factor of the submodule is Using the conventional holding factor K a (i.e. conventional retention factor),

[0104] If the energy dissipation branch of the submodule is in an unavailable state (i.e., E sm =0), the balancing control strategy of the submodule remains unchanged, and the holding factor of the submodule adopts the conventional holding factor K a , K a is slightly larger than 1, K a Less than 2 and greater than 1.

[0105] If the energy dissipation branch of the submodule is in an available state (i.e., E sm=1), calculate the average number of actions of the energy-discharging branch in the available state Then, the action times deviation ΔS of each energy-discharging branch in the available state is obtained. sm =S sm -S ref .

[0106] For the submodules whose energy-discharging branch is in an available state, according to the action times deviation ΔS of the energy-discharging branch sm Obtain the retention factor of the corresponding submodule. If ΔS sm =0, that is, the action times deviation is equal to 0, indicating that the energy absorbed by the energy dissipation branch of the submodule meets expectations, the submodule's balancing control strategy remains unchanged, and the submodule's holding factor adopts the conventional holding factor K a , K a is a value slightly greater than 1.

[0107] 3) If the energy dissipation branch of the submodule is in an available state (i.e. E sm =1), and the number of actions of the submodule energy dissipation branch is biased, that is, ΔS sm ≠0, use optimization strategy 2, that is, use a dynamically adjusted retention factor based on the deviation size

[0108] Among them, if ΔS sm >0, that is, the deviation of the number of actions is greater than 0, and the number of actions of the energy-discharging branch is positively biased, indicating that the energy absorbed by the energy-discharging branch of the submodule is too large. According to the size of the positive bias of the number of actions of the energy-discharging branch, a holding factor K that is smaller than the conventional holding factor is used as the positive bias holding factor. a -ΔS sm *K b (K b is a value slightly greater than 0), that is, the holding factor of this submodule adopts a positive bias holding factor that is smaller than the conventional holding factor and greater than 0.

[0109] If ΔS sm <0, that is, the deviation of the number of actions is less than 0, and the number of actions of the energy-discharging branch is negatively biased, indicating that the energy absorbed by the energy-discharging branch of the submodule is too small. According to the magnitude of the negative bias of the number of actions of the energy-discharging branch, a holding factor K larger than the conventional holding factor is used as the negative bias holding factor. a -ΔS sm *K b (K b is a value slightly greater than 0), that is, the holding factor of this submodule adopts a negative bias holding factor that is greater than the conventional holding factor.

[0110] 4) Determine the submodule to be put into operation according to the size of the bridge arm current and the number of submodules put into operation, and use the holding factor method to sort the submodules and control the voltage balance.

[0111] After the holding factors of all submodules of the converter valve are determined, the holding factors of these submodules are multiplied by the corresponding submodule capacitor voltages to obtain the product of the input voltages, and the input voltages are sorted from low to high to obtain an input voltage group.

[0112] If the bridge arm current i arm >0, input voltage n with lower input voltage in the input voltage group on sub-modules. If the bridge arm current i arm ≤0, input voltage higher n on submodules.

[0113] The number of submodules put into operation refers to the number of submodules put into operation in the next control cycle of the bridge arm n on .

[0114] like Figure 1 The topological structure diagram of the controllable energy-consuming flexible direct current valve shown in the figure, the flexible direct current valve has 6 bridge arms, and the 6 bridge arms are respectively provided with current transformer L1, current transformer L2, current transformer L3, current transformer L4, current transformer L5 and current transformer L6, each bridge arm has N submodules SM, and the N submodules are SM1, SM2, ..., SMN, and the submodule SM can be a full-bridge or half-bridge submodule. An energy dissipation branch is added to the submodule topology, and the energy dissipation branch includes a power electronic switch and an energy dissipation resistor, and the energy dissipation branch is connected in parallel at both ends of the submodule capacitor.

[0115] When an AC fault occurs at the receiving end of the system, the submodule capacitor voltage rises to the energy consumption branch input setting value, the submodule enters the energy discharge state, turns on the energy discharge branch power electronic switch, the energy discharge resistor discharges energy, and the capacitor voltage decreases. When the submodule capacitor voltage decreases to the energy discharge branch cut-off setting value, the energy discharge branch is temporarily locked. If the fault still exists, the capacitor voltage will rise again to the energy discharge branch input setting value, and the above energy discharge process will be repeated until the fault is cleared or the maximum discharge time of the energy discharge resistor is reached. During the entire fault ride-through process, the submodule controller monitors the operating status of the energy discharge branch.

[0116] like Figure 2 The control variable acquisition and control schematic diagram of the balanced control of the controllable energy-consuming flexible direct current valve submodule shown in the figure, the converter valve controller receives the bridge arm current information uploaded by the 6 bridge arm current transformers and the modulation wave sent by the valve control, and generates the number of 6 bridge arm submodules after calculation, which are transmitted to the bridge arm controller together with the bridge arm current. Together with the capacitor voltage, the available state of the energy dissipation branch and the number of energy dissipation branch actions uploaded by each submodule received by the bridge arm controller, they are used as input conditions to balance the voltage and energy of the submodules, and finally generate the input and removal instructions for each submodule.

[0117] In order to verify the feasibility of the balanced control method provided by the present invention, a simulation comparison was carried out with the traditional balanced control strategy. Figure 4 This is a diagram showing the switching frequency effect of the submodule provided by the present invention. Figure 4 By adopting the submodule balancing control method of the present invention, when a three-phase AC fault occurs at the receiving end under different transmission power levels, the average switching frequency of the submodule during the fault ride-through period is roughly equivalent to that of the traditional balancing strategy, without high-frequency problems or significant increase in switching frequency.

[0118] The simulation shows that when a three-phase AC fault occurs at the receiving end under rated operating conditions, the energy absorption distribution of the sub-module energy dissipation resistor in the bridge arm is obtained by using the traditional balanced control strategy and the strategy of the present invention respectively. Figure 5 It can be clearly seen that when a fault occurs at 3s, under the traditional balancing control strategy, the submodule energy dissipation resistance absorbs between 42kJ (kilojoules) and 67kJ, and the energy fluctuation range is large. The strategy of the present invention absorbs the energy dissipation resistance of the submodule between 49kJ and 51kJ, which significantly improves the energy balancing effect of the submodule.

[0119] An embodiment of a balanced control system of a controllable energy-consuming flexible direct current converter valve submodule:

[0120] A balanced control system for a controllable energy-consuming flexible direct current converter valve submodule includes a processor, and the processor is used to execute a computer program to implement the steps of a balanced control method for a controllable energy-consuming flexible direct current converter valve submodule. The balanced control method for a controllable energy-consuming flexible direct current converter valve submodule has been described in detail in an embodiment of a balanced control method for a controllable energy-consuming flexible direct current converter valve submodule, and will not be repeated here.

Claims

1. A balanced control method for a controllable energy-consuming flexible direct current converter valve submodule, characterized in that: The steps include: After the holding factors of all submodules of the flexible DC converter valve are determined, the product of the capacitor voltage of each submodule and the corresponding holding factor constitutes an input voltage group; If the bridge arm current of the converter valve is greater than 0, then select from the input voltage group: the submodule with the smaller product of the number of input submodules of the bridge arm in the next control cycle to be input; If the bridge arm current is less than or equal to 0, then a submodule with a larger product of the number of submodules put into operation is selected from the put-in voltage group and put into operation; The retention factor of the normally functioning submodule among all submodules is determined as follows: If the energy-dissipation branch of the submodule is in an unavailable state, or the deviation of the number of actions of the energy-dissipation branch in an available state is equal to 0, the holding factor of the submodule adopts a conventional holding factor slightly greater than 1; If the deviation of the number of actions is greater than 0, the holding factor of the submodule adopts a positive bias holding factor that is less than the conventional holding factor and greater than 0; If the action number deviation is less than 0, the holding factor of the submodule adopts a negative bias holding factor that is greater than the conventional holding factor.

2. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1 is characterized in that: The small products are selected from the input voltage group in order from small to large.

3. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1 is characterized in that: The larger products are selected in the input voltage group in order from larger to smaller.

4. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1, characterized in that: The holding factor of the submodule that is not operating normally among all submodules adopts the holding factor of the previous control cycle.

5. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1, characterized in that: The calculation formula of the positive bias holding factor is as follows: K Z =K a -ΔS sm *K b In the formula, K Z is the positive bias holding factor, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is a value slightly larger than 0, sm is the number of the submodule, sm∈[1,N].

6. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1, characterized in that: The calculation formula of the negative bias holding factor is as follows: K F =K a -ΔS sm *K b In the formula, K F is the negative bias holding factor, K a is the conventional retention factor, ΔS sm is the deviation of the number of actions, K b is a value slightly larger than 0, sm is the number of the submodule, sm∈[1,N].

7. The balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to claim 1, characterized in that: The calculation formula of the action number deviation is as follows: ΔS sm =S sm -S ref In the formula, ΔS sm is the deviation of the number of actions, S sm is the number of times the energy-dissipating branch operates, S ref is the average number of actions of the energy-discharging branch in an available state, sm is the serial number of the submodule, sm∈[1,N], and m is the number of the energy-discharging branch in an available state.

8. A balanced control system for a controllable energy-consuming flexible direct current converter valve submodule, comprising a processor, characterized in that: The processor is used to execute a computer program to implement the steps of the balanced control method of the controllable energy-consuming flexible direct current converter valve submodule according to any one of claims 1 to 7.

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