Control method and control device of bipolar flexible direct current transmission system

Abstract

The present application provides a control method and a control device for a bipolar flexible direct current transmission system. The bipolar flexible direct current transmission system includes energy-consuming equipment and a new energy unit, a bipolar flexible direct current unit and an alternating current grid connected in sequence, and the energy-consuming equipment is connected to the bipolar flexible direct current unit. The control method includes: judging whether the bipolar flexible direct current transmission system is faulty; in the case of a fault in the bipolar flexible direct current transmission system, judging whether the bipolar flexible direct current unit is unipolarly locked or the alternating current grid fails; in the case of a unipolar locking of the bipolar flexible direct current unit or a fault in the alternating current grid, judging whether the bipolar flexible direct current unit has surplus power; in the case of surplus power in the bipolar flexible direct current unit, determining whether to execute energy consumption control or to execute active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption.

Description

Technical Field

[0001] The present application relates to the technical field of flexible direct current power transmission, and in particular to a control method and a control device for a bipolar flexible direct current power transmission system. Background Art

[0002] With the global energy transformation and carbon neutrality goals, countries around the world are accelerating energy transformation, especially by vigorously developing new energy technologies to solve the dilemma of economic development and climate warming. New energy mainly includes wind power, photovoltaics and supporting energy storage or reactive power compensation devices.

[0003] my country's new energy is mainly concentrated in deserts or at sea. Deserts and offshore new energy show a trend of large-scale development and centralized transmission. Considering that deserts and offshore are at the end of the power grid, the use of bipolar flexible direct current transmission has gradually become a development trend. The offshore wind power being planned abroad is all transmitted via bipolar flexible direct current.

[0004] However, due to the inertia of new energy, a failure in one pole of the converter may cause the healthy pole to trip due to overvoltage due to power accumulation, and the receiving power grid may cause overvoltage tripping due to power accumulation at both poles, affecting the safe operation of the equipment and the reliable operation of the project.

[0005] At present, the project adopts energy dissipation devices with the same capacity as bipolar power to absorb the surplus power, which are usually installed on the AC side or DC side of the sending end. For the bipolar flexible DC transmission system, the installation of DC energy dissipation devices cannot solve the problem of single-pole blocking of parallel operation of new energy at the sending end, and the AC side of the sending end is generally used for energy dissipation. At present, whether it is AC energy dissipation or DC energy dissipation, the cost is high, and the subsequent maintenance is troublesome. There is also a phenomenon that the flexible DC cannot be fault-crossed and blocked due to the unavailability of energy dissipation.

[0006] The above information disclosed in the Background section is only for enhancement of understanding of the background of the present application and therefore it may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0007] In order to solve the above problems, the present application proposes a control method and a control device for a bipolar flexible direct current transmission system.

[0008] According to the first aspect of the present application, at least one embodiment of the present application provides a control method for a bipolar flexible direct current transmission system, wherein the bipolar flexible direct current transmission system comprises an energy-consuming device and a new energy unit, a bipolar flexible direct current unit and an alternating current grid connected in sequence, wherein the energy-consuming device is connected to the bipolar flexible direct current unit, wherein the bipolar flexible direct current unit comprises a sending end and a receiving end, wherein the sending end and the receiving end respectively comprise a positive electrode unit and a negative electrode unit, wherein the control method comprises:

[0009] Determining whether the bipolar flexible direct current power transmission system is faulty;

[0010] In case of a fault in the bipolar flexible DC transmission system, determine whether the bipolar flexible DC unit is unipolarly locked; in case of unipolar locking of the bipolar flexible DC unit, determine whether surplus power occurs in the healthy pole of the bipolar flexible DC unit; in case of surplus power in the healthy pole of the bipolar flexible DC unit, determine whether to perform energy consumption control or send-end active AC voltage control based on the relationship between the surplus power and the maximum available power for energy consumption; or

[0011] In the event of a fault in the bipolar flexible DC transmission system, determine whether the AC power grid fails; in the event of a fault in the AC power grid, determine whether the bipolar flexible DC unit has surplus power; in the event of surplus power in the bipolar flexible DC unit, determine whether to execute energy consumption control or send-end active AC voltage control based on the relationship between the surplus power and the maximum available power for energy consumption.

[0012] According to some embodiments, the capacity of the energy-consuming equipment is less than or equal to the single-pole rated capacity of the bipolar flexible DC unit.

[0013] According to some embodiments, the energy consuming device comprises at least one energy consuming branch.

[0014] According to some embodiments, when the bipolar flexible DC unit is unipolarly locked, determining whether a healthy pole of the bipolar flexible DC unit has surplus power includes:

[0015] When the first indicator of the healthy pole is higher than a first threshold, determining that surplus power occurs in the healthy pole;

[0016] The first indicator includes at least one of a DC voltage of the healthy pole, a voltage of each bridge arm submodule in the healthy pole, and an average voltage of each bridge arm submodule in the healthy pole.

[0017] According to some embodiments, when the bipolar flexible DC unit is unipolarly locked, determining whether a healthy pole of the bipolar flexible DC unit has surplus power includes:

[0018] calculating the surplus power of the sound pole;

[0019] When the surplus power of the healthy pole is greater than zero, it is determined that the bipolar flexible DC unit has surplus power.

[0020] According to some embodiments, the calculating the surplus power of the healthy pole includes:

[0021] In the case where the first power is greater than the second power, determining the surplus power of the healthy pole as the difference between the first power and the second power;

[0022] When the first power is less than or equal to the second power, determining the surplus power of the healthy pole to be zero;

[0023] The first power is the power transmitted from the new energy unit to the sending end of the bipolar flexible DC unit before the bipolar flexible DC transmission system fails, and the second power is the maximum transmittable power of the healthy pole.

[0024] According to some embodiments, further comprising:

[0025] Determine the maximum transmittable power of the healthy pole according to the maximum transmission power limit of the sending end of the healthy pole and the maximum transmission power limit of the receiving end of the healthy pole,

[0026] P sp_max =min{P sendmax |P invmax1}

[0027] Among them, P sp_max is the maximum transmittable power of the healthy pole, P sendmax is the maximum transmission power limit of the sending end of the healthy pole, P invmax1 is the maximum transmission power limit of the receiving end of the healthy pole.

[0028] According to some embodiments, when a fault occurs in the AC power grid, determining whether the bipolar flexible DC unit has surplus power includes:

[0029] When the second indicator of the bipolar flexible DC unit is higher than the second threshold, determining that the bipolar flexible DC unit has surplus power;

[0030] Among them, the second indicator includes at least one of the DC voltage of the positive unit, the DC voltage of the negative unit, the voltage of each of the positive unit bridge arm submodules, the average voltage of the positive unit bridge arm submodules, the voltage of each of the negative unit bridge arm submodules and the average voltage of the negative unit bridge arm submodules.

[0031] According to some embodiments, when a fault occurs in the AC power grid, determining whether the bipolar flexible DC unit has surplus power includes:

[0032] Calculating the surplus power of the bipolar flexible DC unit;

[0033] When the surplus power of the bipolar flexible DC unit is greater than zero, it is determined that the bipolar flexible DC unit has surplus power.

[0034] According to some embodiments, the calculating the surplus power of the bipolar flexible DC unit includes:

[0035] When the first power is greater than the third power, determining the surplus power of the bipolar flexible DC unit as the difference between the first power and the third power;

[0036] When the first power is less than or equal to the third power, determining that the surplus power of the bipolar flexible DC unit is zero;

[0037] Among them, the first power is the power transmitted by the new energy unit to the sending end of the bipolar flexible DC unit before the bipolar flexible DC transmission system fails, and the third power is the maximum transmittable power of the receiving end.

[0038] According to some embodiments, the calculation method of the maximum transmittable power of the receiving end includes:

[0039]

[0040] Where: P invmax2 is the maximum transmittable power of the receiving end, U inv is the effective value of the receiving terminal voltage, I invmax The maximum operating current allowed by the electrical equipment at the receiving end, I invq is the reactive current value emitted by the receiving end according to the demand of the AC power grid, and k is the number of converter valve groups operating in the bipolar flexible DC power transmission system.

[0041] According to some embodiments, further comprising:

[0042] The maximum available power of energy consumption is determined according to the current AC voltage or rated voltage of the sending end and the available energy consumption equivalent resistance,

[0043]

[0044] Among them, P chopp_max (U rec ) is the maximum available power of the energy consumption, U rec_n is the current AC voltage of the sending end or the rated value of the rated voltage, and R is the available energy consumption equivalent resistance.

[0045] According to some embodiments, determining whether to perform energy consumption control or to perform sending-end active AC voltage control according to the relationship between the surplus power and the maximum available power for energy consumption includes:

[0046] When the surplus power does not exceed the maximum available power of the energy consumption, energy consumption control is performed to put the energy consumption branch of the energy consumption device with a capacity corresponding to the surplus power into use.

[0047] According to some embodiments, when surplus power occurs at the healthy pole of the bipolar flexible DC unit and the surplus power is greater than the maximum available power for energy consumption, determining whether to perform energy consumption control or to perform sending-end active AC voltage control according to the relationship between the surplus power and the maximum available power for energy consumption includes:

[0048] Determine the AC voltage setting value of the sending end of the healthy pole according to the low voltage ride-through power characteristics, energy consumption ride-through power of the new energy unit and the maximum transmittable power of the healthy pole;

[0049] Among them, the difference between the low voltage ride-through power characteristic of the new energy unit and the energy consumption ride-through power is less than or equal to the maximum transmittable power of the healthy pole.

[0050] According to some embodiments, when the bipolar flexible DC unit has surplus power and the surplus power is greater than the maximum available power for energy consumption, determining whether to perform energy consumption control or to perform sending-end active AC voltage control according to the relationship between the surplus power and the maximum available power for energy consumption includes:

[0051] Determine the AC voltage setting value at the sending end according to the low voltage ride-through power characteristics, energy consumption ride-through power of the new energy unit and the maximum transmittable power of the receiving end;

[0052] Among them, the difference between the low voltage ride-through power characteristic of the new energy unit and the energy consumption ride-through power is less than or equal to the maximum transmittable power of the receiving end.

[0053] According to some embodiments, further comprising:

[0054] Determining the low voltage ride through power characteristics according to the active current characteristics of the new energy low frequency power transmission system; or

[0055] Determine the low voltage ride through power characteristics according to the dynamic reactive current characteristics of the new energy low frequency power transmission system,

[0056]

[0057] Among them, f recu2p is the low voltage ride-through power characteristic of the new energy unit, U rec is the effective value of the AC voltage at the sending end, I sacm is the maximum current limited by the new energy unit during fault ride-through, f recu2Iq is the dynamic reactive current characteristic.

[0058] According to some embodiments, further comprising:

[0059] The energy consumption ride-through power is determined according to the effective value of the AC voltage at the sending end and the available energy consumption equivalent resistance,

[0060]

[0061] Among them, P chopp is the energy consumption ride-through power, U rec is the effective value of the AC voltage at the sending end, and R is the available energy consumption equivalent resistance.

[0062] According to some embodiments, the maximum transmittable power of the healthy pole is calculated by:

[0063]

[0064] Among them, P sp_max (U rec ) is the maximum transmittable power of the healthy pole, U rec is the effective value of the AC voltage at the sending end, I recmax is the maximum operating current or maximum through-current allowed by the electrical equipment at the sending end, I recq It is the reactive current value emitted by the sending end according to the demand of the AC power grid.

[0065] According to some embodiments, performing active AC voltage control at the sending end includes:

[0066] Control the AC voltage reference value of the sending end to the sending end AC voltage set value.

[0067] According to some embodiments, controlling the AC voltage reference value of the sending end to the sending end AC voltage setting value includes:

[0068] Control a first state quantity to obtain an AC voltage setting value of the sending end; wherein the first state quantity includes at least one of the input power of the bipolar flexible DC power transmission system, the DC voltage of the bipolar flexible DC power transmission system, the voltage of each of the bipolar flexible DC unit bridge arm submodules, and the average voltage of the bipolar flexible DC unit bridge arm submodule;

[0069] The control method used to control the first state quantity includes at least one of PI control, PID control and PR control.

[0070] According to the second aspect of the present application, at least one embodiment of the present application provides a control device for a bipolar flexible direct current transmission system, the control device being used to execute the control method as described in any one of the first aspects, the control device comprising:

[0071] A fault judgment unit is used to judge whether the bipolar flexible DC power transmission system is faulty; in the case of a fault in the bipolar flexible DC power transmission system, judge whether the bipolar flexible DC unit is unipolarly locked or whether the AC power grid is faulty; in the case of a unipolarly locked bipolar flexible DC unit or a fault in the AC power grid, judge whether the bipolar flexible DC unit has surplus power;

[0072] A comparison unit, used for judging whether the surplus power is greater than the maximum available power of energy consumption when the bipolar flexible DC unit has surplus power;

[0073] The execution unit is used to execute energy consumption control or active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption.

[0074] Through the above exemplary embodiments, the control method and control device of a bipolar flexible direct current transmission system provided by the present application have at least one of the following beneficial effects.

[0075] The present application provides a low-cost control method for a bipolar flexible direct current transmission system, which only requires the configuration of energy-consuming devices that are less than or equal to the rated capacity of the single pole. When the energy-consuming devices can meet the surplus power range, it is possible to achieve fault crossing by only putting the energy-consuming devices into use to consume the surplus power in the case of a single-pole fault at the sending end and the receiving end. When the surplus power is greater than the capacity of the energy-consuming device or the energy-consuming device is unavailable, full crossing of the sending and receiving end faults can also be achieved through energy consumption control and active AC voltage control at the sending end. The configuration capacity of the energy-consuming devices of the bipolar flexible direct current transmission system is greatly reduced. At the same time, when the capacity of the energy-consuming devices is insufficient or even unavailable, the fault crossing requirements can be met through active AC voltage, which greatly improves the system operation reliability. At the same time, a certain proportion of energy-consuming devices are configured to reduce the number of times the fan enters low-crossing.

[0076] The present application provides a low-cost control method for a bipolar flexible direct current transmission system. According to the fault probability of the bipolar flexible direct current transmission system, 90% of the single-phase faults in the power grid can be achieved by only investing in energy-consuming equipment. According to the utilization rate of new energy, most bipolar flexible direct current transmission systems operate below 50% of the rated power. Therefore, only single-pole energy-consuming equipment needs to be configured to achieve fault ride-through. There is no need to actively reduce the AC voltage to force the new energy unit to enter low-voltage ride-through. The coordination of the bipolar flexible direct current transmission system is simple, and the control is concise and efficient.

[0077] The present application provides a control method and a control device for a high-reliability bipolar flexible direct current transmission system. When energy-consuming equipment is unavailable or a three-phase fault occurs in a new energy unit, fault crossing can be achieved through active AC voltage control technology, reflecting the versatility of the bipolar flexible direct current transmission system, which can be used with or without energy-consuming equipment.

[0078] It should be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] By describing in detail exemplary embodiments thereof with reference to the accompanying drawings, the above and other objects, features and advantages of the present application will become more apparent. The accompanying drawings described below are only some embodiments of the present application, and are not intended to limit the present application.

[0080] Figure 1 A schematic diagram of a bipolar flexible direct current transmission system is shown according to an exemplary embodiment;

[0081] Figure 2 Another embodiment of a schematic diagram of an exemplary bipolar flexible direct current transmission system is shown;

[0082] Figure 3 A flow chart showing a control method of a bipolar flexible direct current transmission system according to an exemplary embodiment;

[0083] Figure 4 A schematic diagram of a control device of a bipolar flexible direct current transmission system is shown according to an exemplary embodiment. DETAILED DESCRIPTION

[0084] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0085] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of these specific details, or other modes, components, materials, devices, etc. may be adopted. In these cases, known structures, methods, devices, implementations, materials or operations will not be shown or described in detail.

[0086] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0087] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0088] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of example embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing the present application, and therefore cannot be used to limit the scope of protection of the present application.

[0089] Figure 1 A schematic diagram of a bipolar flexible direct current transmission system is shown according to an exemplary embodiment.

[0090] See also Figure 1 The bipolar flexible direct current transmission system includes a new energy unit 100 , a bipolar flexible direct current unit 200 , an energy consuming device 120 and an alternating current grid 190 .

[0091] According to an exemplary embodiment, the bipolar flexible DC unit 200 includes a sending end, a receiving end, and a bipolar DC connection 150. The sending end and the receiving end are connected by the bipolar DC connection 150. The sending end includes a sending end AC bus 110, a first positive unit 130, and a first negative unit 140. The receiving end includes a receiving end AC bus 180, a second positive unit 160, and a second negative unit 170.

[0092] According to an exemplary embodiment, the new energy unit 100 is connected to the sending-end AC bus 110 of the bipolar flexible DC unit 200. The sending-end AC bus 110 is connected to one end of the bipolar DC connection 150 through the first positive unit 130 and the first negative unit 140, and the other end of the bipolar DC connection 150 is connected to the second positive unit 160 and the second negative unit 170, and then connected to the receiving-end AC bus 180. The receiving-end AC bus 180 is connected to the AC grid 190. The first positive unit 130 and the first negative unit 140 are operated in cascade. The second positive unit 160 and the second negative unit 170 are operated in cascade. The energy-consuming device 120 is connected to the sending-end AC bus 110.

[0093] According to some embodiments, the first positive unit 130 includes a transformer and a positive converter, the first negative unit 140 includes a transformer and a negative converter, and the sending-end AC bus 110 is connected to the double-polar DC connection 150 after being connected to the positive converter through the transformer of the first positive unit 130. The sending-end AC bus 110 is connected to the double-polar DC connection 150 after being connected to the negative converter through the transformer of the first negative unit 140. The second positive unit 160 includes a transformer and a positive converter, and the second negative unit 160 includes a transformer and a negative converter. The receiving-end AC bus 180 is connected to the double-polar DC connection 150 after being connected to the positive converter through the transformer of the second positive unit 160. The receiving-end AC bus 180 is connected to the double-polar DC connection 150 after being connected to the negative converter through the transformer of the second negative unit 170.

[0094] According to some embodiments, the new energy unit 110 includes a photovoltaic system and a matching energy storage system, a wind power system and a matching energy storage system, or a wind-solar hybrid system and a matching energy storage system.

[0095] According to some embodiments, the capacity of the energy consuming device 120 is less than or equal to the single-pole rated capacity of the bipolar flexible DC unit 200. For example, the rated capacity of the energy consuming device 120 is less than or equal to the rated capacity of the first positive unit 130 at the sending end or the first negative unit 140 at the sending end.

[0096] According to some embodiments, the energy consumption device 120 configures an energy consumption branch according to the capacity, and the energy consumption device 120 includes at least one energy consumption branch. The energy consumption branch includes a transformer, a switch device and / or a resistor. The switch device includes a thyristor, an IGBT and / or a power electronic switch.

[0097] According to some embodiments, the first positive electrode unit 130 , the first negative electrode unit 140 , the second positive electrode unit 160 , and the second negative electrode unit 170 include a single converter valve group or a cascaded high-low pressure dual valve group.

[0098] According to an exemplary embodiment, the bipolar DC connection 150 includes a positive line, a negative line, and a grounding electrode. The positive line is connected between the first positive unit 130 and the second positive unit 160, and the negative line is connected between the first negative unit 140 and the second negative unit 170. The connection midpoint of the first positive unit 130 and the first negative unit 140 is grounded, and the connection midpoint of the second positive unit 160 and the second negative unit 170 is grounded.

[0099] Figure 2 Another embodiment of a schematic diagram of an exemplary bipolar flexible direct current transmission system is shown.

[0100] See also Figure 2The dual-polarity DC connection 150' includes a positive line, a negative line and a metal return line. The connection midpoint of the first positive unit 130 and the first negative unit 140 is connected to one end of the metal return line, and the connection midpoint of the second positive unit 160 and the second negative unit 170 is connected to the other end of the metal return line. The metal return line is grounded.

[0101] Figure 3 A flow chart of a control method for a bipolar flexible direct current transmission system according to an exemplary embodiment is shown.

[0102] See also Figure 3 , the control method of the bipolar flexible direct current transmission system comprises the following steps:

[0103] In step S1, it is determined whether the bipolar flexible direct current transmission system is faulty.

[0104] According to the exemplary embodiment, it is determined whether the bipolar flexible direct current power transmission system is faulty. If the bipolar flexible direct current power transmission system is faulty, step S2 is executed.

[0105] In step S2, it is determined whether the fault of the bipolar flexible DC power transmission system causes the unipolar converter valve of the bipolar flexible DC unit to be locked.

[0106] According to the example embodiment, in the event of a bipolar flexible DC transmission system fault, it is determined whether the bipolar flexible DC transmission system fault causes the bipolar flexible DC unit unipolar converter valve to be locked, and if so, step S3 is executed; if not, step S7 is executed.

[0107] In step S3, it is determined whether a healthy pole of the bipolar flexible DC unit has surplus power.

[0108] According to an exemplary embodiment, when a fault in a bipolar flexible DC power transmission system causes a unipolar converter valve of a bipolar flexible DC unit to be locked, it is determined whether a healthy pole of the bipolar flexible DC unit has surplus power. If a healthy pole has surplus power, step S4 is performed. If no surplus power occurs, step S2 is performed.

[0109] For example, if a bipolar flexible DC transmission system fails, causing the converter valve of the positive unit in the bipolar flexible DC unit to be locked, then the negative unit will be a healthy pole.

[0110] According to some embodiments, a method for determining whether a healthy pole of a bipolar flexible DC unit has surplus power includes:

[0111] Method 1, when the first indicator of the healthy pole is higher than the first threshold, it is determined that the healthy pole has surplus power. The first indicator includes at least one of the DC voltage of the healthy pole, the voltage of each bridge arm submodule in the healthy pole, and the average voltage of each bridge arm submodule in the healthy pole. The first threshold can be set by oneself.

[0112] Method 2, calculating the surplus power of the healthy pole; when the surplus power is greater than zero, determining that the bipolar flexible DC unit has surplus power.

[0113] The calculating of the surplus power of the healthy pole includes: when the first power is greater than the second power, determining the surplus power to be the difference between the first power and the second power; when the first power is less than or equal to the second power, determining the surplus power to be zero;

[0114] Among them, the first power is the power transmitted from the new energy unit to the sending end of the bipolar flexible DC unit before the failure of the bipolar flexible DC transmission system, and the second power is the maximum transmittable power of the healthy pole.

[0115] Further, calculating the maximum transmittable power of the healthy pole includes: determining the maximum transmittable power of the healthy pole according to the maximum transmittable power limit of the sending end of the healthy pole and the maximum transmittable power limit of the receiving end of the healthy pole. The smaller of the maximum transmittable power limit of the sending end of the healthy pole and the maximum transmittable power limit of the receiving end of the healthy pole is taken as the maximum transmittable power of the healthy pole,

[0116] P sp_max =min{P sendmax |P invmax1}

[0117] Among them, P sp_max is the maximum transmittable power of a sound pole, P sendmax is the maximum transmission power limit of the sending end of the healthy pole, P invmax1 It is the maximum transmission power limit of the receiving end of a healthy pole.

[0118] In step S4, it is determined whether the surplus power is greater than the maximum available power.

[0119] According to an exemplary embodiment, when surplus power occurs in the healthy pole of the bipolar flexible DC unit, it is determined whether the surplus power is greater than the maximum available power for energy consumption, and if so, step S5 is executed. If the surplus power is less than the maximum available power for energy consumption, step S6 is executed.

[0120] According to an exemplary embodiment, the maximum available power of energy consumption is calculated as follows: the maximum available power of energy consumption is determined according to the current AC voltage or rated voltage of the sending end and the available energy consumption equivalent resistance:

[0121]

[0122] Among them, P chopp_max (U rec ) is the maximum available power, U rec_nis the current AC voltage at the sending end or the rated value of the rated voltage, and R is the available energy dissipation equivalent resistance.

[0123] In step S5, active AC voltage control at the sending end is performed.

[0124] According to an example embodiment, when the surplus power is greater than the maximum available power of energy consumption, active AC voltage control at the sending end is performed, including: determining the sending end AC voltage setting value of the healthy pole; controlling the sending end AC voltage reference value of the healthy pole to the sending end AC voltage setting value of the healthy pole.

[0125] According to some embodiments, the calculation method of the AC voltage setting value of the sending end of the healthy pole is: according to the low voltage ride-through power characteristic f of the new energy unit recu2p (U rec ), energy consumption through power P chopp (U rec ) and the maximum transmittable power P of a healthy pole sp_max (U rec ), determine the AC voltage setting value of the sending end of the healthy pole.

[0126] Among them, the difference between the low voltage ride-through power characteristic of the new energy unit and the energy consumption ride-through power is less than or equal to the maximum transmittable power of the sound pole.

[0127] f recu2p (U rec )-P chopp (U rec )≤P sp_max (U rec )

[0128] Furthermore, the low voltage ride through power characteristics of renewable energy can be derived through the dynamic reactive current characteristics or active current characteristics of renewable energy.

[0129] For example, the low voltage ride-through power characteristics are determined based on the dynamic reactive current characteristics of the new energy low frequency transmission system.

[0130]

[0131] Among them, f recu2p is the low voltage ride-through power characteristic of the new energy unit, U rec is the effective value of the AC voltage at the sending end, I sacm is the maximum current limited by the new energy unit during fault ride-through, It is the dynamic reactive current characteristic.

[0132] Furthermore, the energy consumption through power is determined according to the effective value of the AC voltage at the sending end and the available energy consumption equivalent resistance.

[0133]

[0134] Among them, P chopp is the energy consumption through power, U rec is the effective value of the AC voltage at the sending end, and R is the available energy-consuming equivalent resistance.

[0135] Furthermore, the maximum transmittable power of a sound pole is calculated as:

[0136]

[0137] Among them, P sp_max (U rec ) is the maximum transmittable power of a sound pole, U rec is the effective value of the AC voltage at the sending end, I recmax It is the maximum operating current or maximum through current allowed by the electrical equipment at the sending end, I recq It is the reactive current value emitted by the sending end according to the demand of the AC power grid.

[0138] According to some embodiments, controlling the reference value of the sending-end AC voltage of the healthy pole to the setting value of the sending-end AC voltage of the healthy pole includes: controlling the first state quantity to obtain the setting value of the AC voltage of the healthy pole.

[0139] Among them, the first state quantity includes at least one of the input power of the bipolar flexible DC transmission system, the DC voltage of the bipolar flexible DC transmission system, the voltage of each bipolar flexible DC unit bridge arm submodule and the average voltage of the bipolar flexible DC unit bridge arm submodule.

[0140] The control method used to control the first state quantity includes at least one of PI control, PID control and PR control.

[0141] For example, taking the control of the average voltage of the submodule as an example, the AC voltage set value can be generated by PI control, PID control and / or PR control after subtracting the rated voltage of the submodule from the current average voltage of the submodule.

[0142] In step S6, energy consumption control is performed and the energy consumption branch is put into operation.

[0143] According to an exemplary embodiment, when the surplus power is less than or equal to the maximum available power for energy consumption, energy consumption control is performed, and energy consumption branches of the energy consumption device with a capacity corresponding to the surplus power are put into use.

[0144] In step S7, it is determined whether a fault occurs in the AC power grid.

[0145] According to the exemplary embodiment, in the case of a fault in the bipolar flexible direct current transmission system, it is determined whether the AC power grid is faulty. If the AC power grid is faulty, step S8 is performed; if the AC power grid is not faulty, step S1 is performed.

[0146] In step S8, it is determined whether the bipolar flexible DC unit has surplus power.

[0147] According to the exemplary embodiment, when an AC power grid fails, it is determined whether the bipolar flexible DC unit has surplus power. If surplus power occurs, step S9 is executed; if no surplus power occurs, step S7 is executed.

[0148] According to some embodiments, a method for determining whether a bipolar flexible DC unit has surplus power includes:

[0149] Method 1, when the second indicator of the bipolar flexible DC unit is higher than the second threshold, determining that the bipolar flexible DC unit has surplus power. The second indicator includes at least one of the DC voltage of the positive unit, the DC voltage of the negative unit, the voltage of each bridge arm submodule of the positive unit, the average voltage of the bridge arm submodule of the positive unit, the voltage of each bridge arm submodule of the negative unit, and the average voltage of the bridge arm submodule of the negative unit.

[0150] Method 2, calculating the surplus power of the bipolar flexible DC unit; when the surplus power is greater than zero, determining that the bipolar flexible DC unit has surplus power.

[0151] The calculation of the surplus power of the bipolar flexible DC unit includes: when the first power is greater than the third power, determining the surplus power as the difference between the first power and the third power; when the first power is less than or equal to the third power, determining the surplus power to be zero. The first power is the power transmitted from the new energy unit to the sending end of the bipolar flexible DC unit before the bipolar flexible DC transmission system fails, and the third power is the maximum transmittable power of the receiving end.

[0152] Furthermore, the maximum transmittable power of the receiving end is calculated as follows:

[0153]

[0154] Where: P invmax2 is the maximum transmittable power at the receiving end, U inv is the effective value of the receiving terminal voltage, I invmax The maximum operating current allowed by the electrical equipment at the receiving end, I invq is the reactive current value emitted by the receiving end according to the demand of the AC power grid, and k is the number of converter valve groups operating in the bipolar flexible DC transmission system.

[0155] In step S9, it is determined whether the surplus power is greater than the maximum available power.

[0156] According to an exemplary embodiment, when the bipolar flexible DC unit has surplus power, it is determined whether the surplus power is greater than the maximum available power. If the surplus power is greater than the maximum available power, step S10 is executed. If the surplus power is less than the maximum available power, step S6 is executed.

[0157] According to some embodiments, the maximum available power of energy consumption is calculated as follows: the maximum available power of energy consumption is determined according to the current AC voltage or rated voltage of the sending end and the available energy consumption equivalent resistance:

[0158]

[0159] Among them, P chopp_max (U rec ) is the maximum available power, U rec_n is the current AC voltage at the sending end or the rated value of the rated voltage, and R is the available energy dissipation equivalent resistance.

[0160] In step S10, active AC voltage control at the sending end is performed.

[0161] According to an example embodiment, when the surplus power is greater than the maximum available power, active AC voltage control at the sending end is performed, including: determining a sending end AC voltage setting value; and controlling a sending end AC voltage reference value to the sending end AC voltage setting value.

[0162] According to some embodiments, the calculation method of the AC voltage setting value at the sending end is as follows: according to the low voltage ride-through power characteristic f of the new energy unit recu2p , Energy consumption through power P chopp (U rec ) and the maximum transmittable power P at the receiving end invmax2 , determine the setting value of the AC voltage at the sending end.

[0163] Among them, the difference between the low voltage ride-through power characteristic of the new energy unit and the energy consumption ride-through power is less than or equal to the maximum transmittable power of the receiving end.

[0164] f recu2p (U rec )-P chopp (U rec )≤P invmax2

[0165] Furthermore, the low voltage ride through power characteristics of renewable energy can be derived through the dynamic reactive current characteristics or active current characteristics of renewable energy.

[0166] For example, the low voltage ride-through power characteristics are determined based on the dynamic reactive current characteristics of the new energy low frequency transmission system.

[0167]

[0168] Among them, f recu2p is the low voltage ride-through power characteristic of the new energy unit, U rec is the effective value of the AC voltage at the sending end, I sacm is the maximum current limited by the new energy unit during fault ride-through, It is the dynamic reactive current characteristic.

[0169] Furthermore, the energy consumption through power is determined according to the effective value of the AC voltage at the sending end and the available energy consumption equivalent resistance.

[0170]

[0171] Among them, P chopp is the energy consumption through power, U rec is the effective value of the AC voltage at the sending end, and R is the available energy-consuming equivalent resistance.

[0172] Furthermore, the maximum transmittable power of the receiving end is calculated as follows:

[0173]

[0174] Where: P invmax2 is the maximum transmittable power at the receiving end, U inv is the effective value of the receiving terminal voltage, I invmax The maximum operating current allowed by the electrical equipment at the receiving end, I invq is the reactive current value emitted by the receiving end according to the demand of the AC power grid, and k is the number of converter valve groups operating in the bipolar flexible DC transmission system.

[0175] According to some embodiments, controlling the sending-end AC voltage reference value to the sending-end AC voltage setting value includes: controlling a first state quantity to obtain the sending-end AC voltage setting value.

[0176] Among them, the first state quantity includes at least one of the input power of the bipolar flexible direct current transmission system, the direct current voltage of the bipolar flexible direct current transmission system, the voltage of each bridge arm submodule of the bipolar flexible direct current unit and the average voltage of each bridge arm submodule.

[0177] The control method used to control the first state quantity includes at least one of PI control, PID control and PR control.

[0178] For example, taking the control of the average voltage of the submodule as an example, the AC voltage set value can be generated by PI control, PID control and / or PR control after subtracting the rated voltage of the submodule from the current average voltage of the submodule.

[0179] According to some embodiments, when the surplus power is greater than the maximum available power of energy consumption, the sending end active AC voltage control can be performed after the energy consumption equipment of full capacity is put into use. When the energy consumption equipment fails and is unavailable, the sending end active AC voltage control can also be performed directly to achieve fault ride-through of the bipolar flexible DC transmission system.

[0180] The present application provides a low-cost control method for a bipolar flexible direct current transmission system, which only requires the configuration of energy-consuming devices that are less than or equal to the rated capacity of the single pole. When the energy-consuming devices can meet the surplus power range, it is possible to achieve fault crossing by only putting the energy-consuming devices into use to consume the surplus power in the case of a single-pole fault at the sending end and the receiving end. When the surplus power is greater than the capacity of the energy-consuming device or the energy-consuming device is unavailable, full crossing of the sending and receiving end faults can also be achieved through energy consumption control and active AC voltage control at the sending end. The configuration capacity of the energy-consuming devices of the bipolar flexible direct current transmission system is greatly reduced. At the same time, when the capacity of the energy-consuming devices is insufficient or even unavailable, the fault crossing requirements can be met through active AC voltage, which greatly improves the system operation reliability. At the same time, a certain proportion of energy-consuming devices are configured to reduce the number of times the fan enters low-crossing.

[0181] The present application provides a low-cost control method for a bipolar flexible direct current transmission system. According to the fault probability of the bipolar flexible direct current transmission system, 90% of the single-phase faults in the power grid can be achieved by only investing in energy-consuming equipment. According to the utilization rate of new energy, most bipolar flexible direct current transmission systems operate below 50% of the rated power. Therefore, only single-pole energy-consuming equipment needs to be configured to achieve fault ride-through. There is no need to actively reduce the AC voltage to force the new energy unit to enter low-voltage ride-through. The coordination of the bipolar flexible direct current transmission system is simple, and the control is concise and efficient.

[0182] The present application provides a control method for a high-reliability bipolar flexible direct current transmission system. When energy-consuming equipment is unavailable or a three-phase fault occurs in a new energy unit, fault crossing can be achieved through active AC voltage control technology, reflecting the versatility of the bipolar flexible direct current transmission system, which can be used with or without energy-consuming equipment.

[0183] Figure 4 A schematic diagram of a control device of a bipolar flexible direct current transmission system is shown according to an exemplary embodiment.

[0184] See also Figure 4 The control device of the bipolar flexible direct current transmission system includes a collection unit 401 , a fault judgment unit 402 , an execution unit 403 , a comparison unit 404 and a calculation and adjustment unit 405 .

[0185] According to the exemplary embodiment, the acquisition unit 401 is used to acquire state information such as voltage and current of the bipolar flexible direct current transmission system.

[0186] The fault judgment unit 402 is used to judge whether the bipolar flexible DC power transmission system is faulty according to the state information collected by the collection unit 401. The fault judgment unit 402 is also used to judge whether the bipolar flexible DC unit is unipolarly locked or whether the AC power grid is faulty when the bipolar flexible DC power transmission system is faulty. The fault judgment unit 402 is also used to judge whether the bipolar flexible DC unit has surplus power when the bipolar flexible DC unit is unipolarly locked or the AC power grid is faulty.

[0187] The calculation and adjustment unit 405 is used to calculate the surplus power and the maximum available power of energy consumption when the bipolar flexible DC unit is unipolarly locked or the AC power grid fails.

[0188] The comparison unit 404 is used to determine whether the surplus power is greater than the maximum available power when the bipolar flexible DC unit has surplus power.

[0189] The execution unit 403 is used to perform energy consumption control or active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption, including:

[0190] When executing energy consumption control, a switching command of the energy-consuming equipment is sent.

[0191] When executing the active AC voltage control at the sending end, the calculation and adjustment unit 405 is used to calculate the AC voltage setting value at the sending end. The execution unit 403 directly or additionally controls the voltage to the AC voltage setting value at the sending end by using at least one of PI control, PID control and PR control through the input power, DC voltage, the voltage of each bridge arm submodule and or the average voltage of each bridge arm submodule, so that the new energy system enters the low voltage ride-through mode.

[0192] It should be clearly understood that the present application describes how to form and use specific examples, but the present application is not limited to any details of these examples. On the contrary, based on the teaching of the content disclosed in the present application, these principles can be applied to many other embodiments.

[0193] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present application, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0194] The exemplary embodiments of the present application are specifically shown and described above. It should be understood that the present application is not limited to the detailed structures, configurations or implementations described herein; on the contrary, the present application is intended to cover various modifications and equivalent configurations included in the spirit and scope of the appended claims.

Claims

1. A control method for a bipolar flexible direct current transmission system, characterized in that: The bipolar flexible DC power transmission system comprises an energy-consuming device and a new energy unit, a bipolar flexible DC unit and an AC power grid connected in sequence, the energy-consuming device is connected to the bipolar flexible DC unit, the bipolar flexible DC unit comprises a sending end and a receiving end, the sending end and the receiving end respectively comprise a positive electrode unit and a negative electrode unit, and the control method comprises: Determining whether the bipolar flexible direct current power transmission system is faulty; In the case of a fault in the bipolar flexible DC power transmission system, determine whether the unipolar converter valve of the bipolar flexible DC unit is locked; in the case of the unipolar converter valve of the bipolar flexible DC unit being locked, determine whether surplus power occurs in the healthy pole of the bipolar flexible DC unit; in the case of surplus power occurring in the healthy pole of the bipolar flexible DC unit, determine whether to perform energy consumption control or active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption; in the case of the surplus power not exceeding the maximum available power of energy consumption, perform energy consumption control and put into use the energy consumption branch of the energy consuming equipment with the capacity corresponding to the surplus power; in the case of the surplus power exceeding the maximum available power of energy consumption, perform active AC voltage control at the sending end, including: Determine the AC voltage setting value of the sending end of the healthy pole according to the low voltage ride-through power characteristic of the new energy unit, the energy ride-through power and the maximum transmittable power of the healthy pole; wherein the difference between the low voltage ride-through power characteristic of the new energy unit and the energy ride-through power is less than or equal to the maximum transmittable power of the healthy pole; Controlling the AC voltage reference value of the sending end to the AC voltage setting value of the sending end; or In the case where the bipolar flexible DC power transmission system fails and does not cause the unipolar converter valve of the bipolar flexible DC unit to be locked, determine whether the AC power grid fails; in the case where the AC power grid fails, determine whether the bipolar flexible DC unit has surplus power; in the case where the bipolar flexible DC unit has surplus power, determine whether to perform energy consumption control or active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption; in the case where the surplus power does not exceed the maximum available power of energy consumption, perform energy consumption control and put into use the energy consumption branch of the energy consuming equipment with a capacity corresponding to the surplus power; in the case where the surplus power exceeds the maximum available power of energy consumption, perform active AC voltage control at the sending end, including: Determine the AC voltage setting value at the sending end according to the low voltage ride through power characteristics, the energy ride through power and the maximum transmittable power of the receiving end of the new energy unit; wherein the difference between the low voltage ride through power characteristics and the energy ride through power of the new energy unit is less than or equal to the maximum transmittable power of the receiving end; Control the AC voltage reference value of the sending end to the sending end AC voltage set value.

2. The control method according to claim 1, characterized in that: The capacity of the energy-consuming equipment is less than or equal to the single-pole rated capacity of the bipolar flexible DC unit.

3. The control method according to claim 2, characterized in that: The energy consuming device includes at least one energy consuming branch.

4. The control method according to claim 1, characterized in that: In the case where the bipolar flexible DC unit is unipolarly locked, judging whether a healthy pole of the bipolar flexible DC unit has surplus power includes: When the first indicator of the healthy pole is higher than a first threshold, determining that surplus power occurs in the healthy pole; The first indicator includes at least one of a DC voltage of the healthy pole, a voltage of each bridge arm submodule in the healthy pole, and an average voltage of each bridge arm submodule in the healthy pole.

5. The control method according to claim 1, characterized in that: In the case where the bipolar flexible DC unit is unipolarly locked, judging whether a healthy pole of the bipolar flexible DC unit has surplus power includes: calculating the surplus power of the sound pole; When the surplus power of the healthy pole is greater than zero, it is determined that the bipolar flexible DC unit has surplus power.

6. The control method according to claim 5, characterized in that: The calculating the surplus power of the healthy pole comprises: In the case where the first power is greater than the second power, determining the surplus power of the healthy pole as the difference between the first power and the second power; When the first power is less than or equal to the second power, determining the surplus power of the healthy pole to be zero; The first power is the power transmitted from the new energy unit to the sending end of the bipolar flexible DC unit before the bipolar flexible DC transmission system fails, and the second power is the maximum transmittable power of the healthy pole.

7. The control method according to claim 6, characterized in that: Also includes: Determine the maximum transmittable power of the healthy pole according to the maximum transmission power limit of the sending end of the healthy pole and the maximum transmission power limit of the receiving end of the healthy pole, P sp_max =min{P sendmax |P invmax1 } Among them, P sp_max is the maximum transmittable power of the healthy pole, P sendmax is the maximum transmission power limit of the sending end of the healthy pole, P invmax1 is the maximum transmission power limit of the receiving end of the healthy pole.

8. The control method according to claim 1, characterized in that: When a fault occurs in the AC power grid, determining whether the bipolar flexible DC unit has surplus power includes: When the second indicator of the bipolar flexible DC unit is higher than the second threshold, determining that the bipolar flexible DC unit has surplus power; Among them, the second indicator includes at least one of the DC voltage of the positive unit, the DC voltage of the negative unit, the voltage of each of the positive unit bridge arm submodules, the average voltage of the positive unit bridge arm submodules, the voltage of each of the negative unit bridge arm submodules and the average voltage of the negative unit bridge arm submodules.

9. The control method according to claim 1, characterized in that: When a fault occurs in the AC power grid, determining whether the bipolar flexible DC unit has surplus power includes: Calculating the surplus power of the bipolar flexible DC unit; When the surplus power of the bipolar flexible DC unit is greater than zero, it is determined that the bipolar flexible DC unit has surplus power.

10. The control method according to claim 9, characterized in that: The calculating the surplus power of the bipolar flexible DC unit includes: When the first power is greater than the third power, determining the surplus power of the bipolar flexible DC unit as the difference between the first power and the third power; When the first power is less than or equal to the third power, determining that the surplus power of the bipolar flexible DC unit is zero; Among them, the first power is the power transmitted by the new energy unit to the sending end of the bipolar flexible DC unit before the bipolar flexible DC transmission system fails, and the third power is the maximum transmittable power of the receiving end.

11. The control method according to claim 10, characterized in that: The calculation method of the maximum transmittable power of the receiving end includes: Where: P invmax2 is the maximum transmittable power of the receiving end, U inv is the effective value of the receiving terminal voltage, I invmax The maximum operating current allowed by the electrical equipment at the receiving end, I invq is the reactive current value emitted by the receiving end according to the demand of the AC power grid, and k is the number of converter valve groups operating in the bipolar flexible DC power transmission system.

12. The control method according to claim 1, characterized in that: Also includes: The maximum available power of energy consumption is determined according to the current AC voltage or rated voltage of the sending end and the available energy consumption equivalent resistance, Among them, P chopp_max (U rec ) is the maximum available power of the energy consumption, U rec_n is the current AC voltage of the sending end or the rated value of the rated voltage, and R is the available energy consumption equivalent resistance.

13. The control method according to claim 1, characterized in that: Also includes: Determining the low voltage ride through power characteristics according to the active current characteristics of the new energy low frequency power transmission system; or Determine the low voltage ride through power characteristics according to the dynamic reactive current characteristics of the new energy low frequency power transmission system, Among them, f recu2p is the low voltage ride-through power characteristic of the new energy unit, U rec is the effective value of the AC voltage at the sending end, I sacm is the maximum current limited by the new energy unit during fault ride-through, is the dynamic reactive current characteristic.

14. The control method according to claim 1, characterized in that: Also includes: The energy consumption ride-through power is determined according to the effective value of the AC voltage at the sending end and the available energy consumption equivalent resistance, Among them, P chopp is the energy consumption ride-through power, U rec is the effective value of the AC voltage at the sending end, and R is the available energy consumption equivalent resistance.

15. The control method according to claim 1, characterized in that: The calculation method of the maximum transmittable power of the sound pole includes: Among them, P sp_max ( U rec ) is the maximum transmittable power of the healthy pole, U rec is the effective value of the AC voltage at the sending end, I recmax is the maximum operating current or maximum through-current allowed by the electrical equipment at the sending end, I recq It is the reactive current value emitted by the sending end according to the demand of the AC power grid.

16. The control method according to claim 1, characterized in that: The step of controlling the AC voltage reference value of the sending end to the AC voltage setting value of the sending end includes: Control a first state quantity to obtain an AC voltage setting value of the sending end; wherein the first state quantity includes at least one of the input power of the bipolar flexible DC power transmission system, the DC voltage of the bipolar flexible DC power transmission system, the voltage of each of the bipolar flexible DC unit bridge arm submodules, and the average voltage of the bipolar flexible DC unit bridge arm submodule; The control method used to control the first state quantity includes at least one of PI control, PID control and PR control.

17. A control device for a bipolar flexible direct current transmission system, the control device being used to execute the control method according to any one of claims 1 to 16, characterized in that: The control device comprises: A fault judgment unit is used to judge whether the bipolar flexible DC power transmission system is faulty; in the case of a fault in the bipolar flexible DC power transmission system, judge whether the bipolar flexible DC unit is unipolarly locked; in the case of a fault in the bipolar flexible DC power transmission system and no unipolar converter valve is locked, judge whether the AC power grid is faulty; in the case of a unipolar converter valve of the bipolar flexible DC unit being locked or a fault in the AC power grid, judge whether the bipolar flexible DC unit has surplus power; A comparison unit, used for judging whether the surplus power is greater than the maximum available power of energy consumption when the bipolar flexible DC unit has surplus power; The execution unit is used to execute energy consumption control or active AC voltage control at the sending end according to the relationship between the surplus power and the maximum available power of energy consumption.

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