High-low voltage ride-through control method of converter multi-machine parallel system and converter multi-machine parallel system

Abstract

The invention provides a high-low voltage ride-through control method for a converter multi-machine parallel system and the converter multi-machine parallel system, and the method comprises the steps: controlling all parallel converters through a parallel operation box in the converter multi-machine parallel system, thereby obtaining a power grid electric signal in a grid-connected operation mode, and achieving the high-low voltage ride-through control of the converter multi-machine parallel system. Judging whether a high-low voltage ride-through condition is met or not according to the power grid electric signal; if yes, controlling the power loop of the parallel operation box to reset; and sending a reset instruction to each converter, wherein the reset instruction is used for instructing each converter to reset the corresponding power loop when monitoring the reset instruction and not monitoring the power grid fault. Through the method, the problem that high and low voltage ride-through cannot be normally completed due to the fact that the detected high and low voltage ride-through moments are inconsistent among multiple machines can be avoided, and therefore it is guaranteed that the high and low voltage ride-through capacity of the converter multi-machine parallel system meets the grid-connected standard requirement.

Description

Technical Field

[0001] The present invention relates to the field of power grid technology, and in particular to a high and low voltage ride through control method and related devices for a converter multi-machine parallel system. Background Art

[0002] High and low voltage ride through refers to the ability of a wind turbine or photovoltaic power generation system to maintain connection with the grid and provide necessary support to help the grid resume stable operation when the grid voltage fluctuates abnormally.

[0003] For the converter, it is necessary to have high and low voltage ride-through detection and protection functions. When the power of a single converter is small, multiple converters are usually connected in parallel to expand capacity to meet market demand. In the parallel scenario, multiple converters in parallel detect inconsistent high and low voltage ride-through times, which results in the high and low voltage ride-through capabilities of the parallel system not meeting the grid connection standard requirements. Summary of the invention

[0004] The embodiment of the present invention provides a high and low voltage ride through control method and related device of a converter multi-machine parallel system to solve the problem of high and low voltage ride through failure of the converter multi-machine parallel system in the prior art.

[0005] In a first aspect, an embodiment of the present invention provides a high and low voltage ride-through control method for a converter multi-machine parallel system, wherein the converter multi-machine parallel system includes a parallel box and a plurality of converters; the parallel box includes an AC bus, the AC side of each converter is connected to the AC bus, and the AC bus is used to connect to a power grid, and the parallel box is communicatively connected to each converter;

[0006] The method is applied to the parallel box, comprising:

[0007] In the grid-connected operation mode, a grid electrical signal is obtained, and whether a high or low voltage ride-through condition is met according to the grid electrical signal;

[0008] If satisfied, the power loop of the parallel box is controlled to be reset; and a reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected.

[0009] In a second aspect, an embodiment of the present invention provides a parallel box, including an AC bus, a first switch, a second switch and a controller, wherein the AC bus is connected to the AC end of each converter respectively, a first end of the first switch and a first end of the second switch are both connected to the AC bus, a second end of the first switch is used to connect to a power grid, and a second end of the second switch is used to connect to a load;

[0010] The controller is used to execute the high and low voltage ride through control method of the converter multi-machine parallel system as described in any one of the first aspects above.

[0011] In a third aspect, an embodiment of the present invention provides a converter multi-machine parallel connection system, comprising a plurality of converters and the parallel connection box as described above.

[0012] The embodiment of the present invention provides a high and low voltage ride-through control method for a converter multi-machine parallel system and a converter multi-machine parallel system. The method controls all parallel converters through a parallel box in the parallel system, thereby obtaining a grid electrical signal in a grid-connected operation mode, and judging whether the high and low voltage ride-through conditions are met according to the grid electrical signal; if met, the power loop of the parallel box is controlled to reset; and a reset instruction is sent to each converter, the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid-related fault is detected. Through the above method, this embodiment can avoid the problem of being unable to complete the high and low voltage ride-through normally due to inconsistent high and low voltage ride-through detection times between multiple machines, thereby ensuring that the high and low voltage ride-through capability of the converter multi-machine parallel system meets the grid-connected standard requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 is a schematic structural diagram of a converter multi-machine parallel system provided by an embodiment of the present invention;

[0015] Figure 2 It is a flow chart for implementing a high and low voltage ride through control method of a converter multi-machine parallel system provided by an embodiment of the present invention;

[0016] Figure 3 is a schematic diagram of the structure of a high and low voltage ride through control device for a converter multi-machine parallel system provided by an embodiment of the present invention;

[0017] Figure 4 It is a schematic diagram of a parallel box provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0019] In the description of the present application specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0020] References to "one embodiment" or "some embodiments" etc. described in the specification of this application mean that one or more embodiments of the present application include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0021] In addition, the “plurality” mentioned in the embodiments of the present application should be interpreted as two or more.

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below in conjunction with the accompanying drawings.

[0023] Figure 1 The schematic diagram of the structure of the converter multi-machine parallel system provided by the embodiment of the present invention. Figure 1 As shown, the inverter multi-machine parallel system includes a parallel box and multiple inverters; the parallel box includes an AC bus, the AC side of each inverter is connected to the AC bus, and the AC bus is used to connect to the power grid, and the parallel box is communicatively connected to each inverter.

[0024] The converter in this embodiment can be an energy storage inverter, a photovoltaic inverter, or an AC to AC converter. The following takes the energy storage inverter as an example to explain the high and low voltage ride-through control method of the converter multi-machine parallel system provided in the embodiment.

[0025] Specifically, Figure 1As shown, the converter multi-machine parallel system includes multiple converters, switches corresponding to each converter, and a parallel box; wherein the AC ends of multiple energy storage inverters are connected to the AC bus AC-BUS in the parallel box through their corresponding switches (KN1, KN2). The parallel box also includes a first switch K1, a second switch K2, a third switch K3, and a controller; the AC bus AC-BUS is connected to the first ends of the first switch K1 and the second switch K2, respectively, the second end of the first switch K1 is connected to one end of the switching switch, the other end of the switching switch is connected to the power grid, and the second end of the second switch K2 is connected to the load; the first end of the third switch K3 is connected to the second end of the first switch K1, and the second end of the third switch K3 is connected to the second end of the second switch K2. wherein, the switch at the AC end of each energy storage inverter can be an electromagnetic switch or a manual switch.

[0026] Each energy storage inverter includes a controller, and the corresponding current transformer circuit is controlled by the controller. The controller in the parallel box is connected to the controllers of each energy storage inverter for controlling the operation of all energy storage inverters from the upper layer. The first switch, the second switch and the third switch can be electromagnetic switches or manual switches. When the first switch, the second switch and the third switch are electromagnetic switches, the parallel box is connected to the first switch and the second switch for controlling the switching state of the first switch and the second switch. Among them, the energy storage inverter can be connected to the controllers of each energy storage inverter via CAN communication / RS485 communication.

[0027] The present embodiment provides a high and low voltage ride-through control method for a converter multi-machine parallel system. The executor of the method is a controller in a parallel box. The parallel box in the converter multi-machine parallel system controls all parallel converters to avoid the problem of failure to normally implement high and low voltage ride-through due to inconsistent high and low voltage ride-through detection times among multiple machines, thereby ensuring that the converter multi-machine parallel system meets the grid-connected standard requirements.

[0028] For details, see Figure 2 , which shows a schematic diagram of the implementation flow of the high and low voltage ride through control method of the converter multi-machine parallel system provided by an embodiment of the present invention, and the process is described in detail as follows:

[0029] S101: In a grid-connected operation mode, a grid electrical signal is obtained, and whether a high or low voltage ride-through condition is met according to the grid electrical signal.

[0030] In this embodiment, low-voltage ride-through capability (LVRT) refers to the ability of the energy storage power generation system to remain connected to the grid and even provide a certain amount of reactive power to the grid to support grid recovery until the grid returns to normal, thereby "crossing" this low voltage time (area). High-voltage ride-through (HVRT) refers to the ability of the energy storage power generation system to remain connected to the grid, continue to operate stably, and meet relevant technical requirements when the grid voltage of the power system increases.

[0031] The requirements for high and low voltage ride-through in an international standard for high and low voltage ride-through are detailed in Table 1:

[0032] Table 1

[0033] Serial number Ratio of fault voltage to rated voltage Fault duration (ms) 1 <0.05 >200 2 0.4-0.45 >1625 3 0.8-0.85 >3000 4 >1.15 >60,000 5 >1.2 >1000

[0034] In order to achieve high and low voltage ride through, when the grid voltage is lower than 0.85U N Or higher than 1.15U N When the inverter enters the high and low voltage ride-through mode, the inverter needs to limit the voltage to 10% P within 100ms. N , when the grid voltage is restored, the active power needs to be restored to the power before the ride-through within 1 second, and the reactive power recovery needs to meet the 10 second first-order filter response; where U N Indicates the rated voltage of the power grid; P N Indicates the rated output power.

[0035] In order to meet the international standards for high and low voltage ride-through and avoid high and low voltage ride-through failures, in this embodiment, when the inverter multi-machine parallel system is connected to the grid and operates, the grid voltage is obtained. If the ratio of the grid voltage to the rated grid voltage is less than 0.85, it is determined that the low voltage ride-through condition is met at this time. If the ratio of the grid voltage to the rated grid voltage is greater than 1.15, it is determined that the high voltage ride-through condition is met at this time.

[0036] In a possible implementation, the specific implementation process of S101 includes:

[0037] Acquiring a voltage signal between the AC bus and the power grid as a first voltage signal;

[0038] Whether a high or low voltage ride-through condition is met is determined according to the first voltage signal.

[0039] Specifically, when the inverter multi-machine parallel system is loaded and the grid voltage drops, the voltage generated by the grid-connected current on the load may be mistaken by the inverter as the grid voltage, resulting in the inverter being unable to detect voltage ride-through, and ultimately leading to ride-through failure. This embodiment can more accurately monitor the grid voltage by setting a voltage sampling device on the line between the AC bus in the parallel box and the grid, avoiding the interference of the voltage generated by the load current on the sampling device on the inverter side, and improving the accuracy of grid voltage detection.

[0040] In this embodiment, when the first voltage signal is lower than the low voltage ride-through threshold or higher than the high voltage ride-through threshold, it is determined that the power grid meets the high and low voltage ride-through condition.

[0041] S102: If the conditions are met, the power loop of the parallel box is controlled to be reset; and a reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected.

[0042] Under normal circumstances, the control loop executed by the parallel box in the parallel system is: after receiving the total power set value of the parallel system, the total power set value is decomposed into the power set values ​​corresponding to each inverter according to the remaining capacity percentage and health status of the batteries corresponding to each energy storage inverter.

[0043] After the parallel box determines the power set value corresponding to each converter, it sends the power set value corresponding to each converter to the controller of the corresponding converter. After receiving the power set value from the parallel box, the controller of each converter executes the control loop: generating a PWM signal to control the converter according to the power set value.

[0044] In order to meet the high and low voltage ride-through requirements, the parallel box resets the power loop after detecting that the grid electrical signal meets the high and low voltage ride-through conditions, and sends the reset command to each converter, so that each converter resets the corresponding power loop when the reset signal is detected and no grid fault is detected.

[0045] In a possible implementation manner, before S102, the method provided in this embodiment further includes:

[0046] When the high and low voltage enable signals are detected, continue to execute the subsequent steps.

[0047] It can be seen from the above embodiments that this embodiment can avoid the problem of failure to normally complete high and low voltage ride-through due to inconsistent high and low voltage ride-through detection times among multiple machines, thereby ensuring that the converter multi-machine parallel system meets the grid connection standard requirements.

[0048] In a possible implementation manner, if the condition in S102 is satisfied, the implementation process of controlling the power loop reset of the parallel box includes:

[0049] If the high and low voltage ride-through conditions are met, the output value of the active power loop of the parallel box is cleared, and the power set value, output value and integral value of the active power loop before clearing are saved.

[0050] In this embodiment, the control loop in the parallel box includes an active power loop, an active power distribution unit, a reactive power loop and a reactive power distribution unit, wherein the power loop includes an active power loop and a reactive power loop; the parallel box obtains the total active power actual value and the total active power set value of the AC bus, and then inputs the total active power actual value and the total active power set value into the active power loop, the active power loop outputs the active control amount, and then inputs the active control amount into the active power distribution unit, the active power distribution unit obtains the active power set value corresponding to each converter based on the remaining capacity percentage and health status of the battery corresponding to each converter; the controller of the converter inputs the active power set value into the active power loop to obtain the corresponding PWM signal. Among them, the active power loop, reactive power loop of the parallel box, the active power loop and reactive power loop of the converter all include PI controllers.

[0051] In this embodiment, as an international standard for high and low voltage ride-through, when the power grid has high and low voltage abnormalities, the active loops of the parallel box and the converter can be reset; the reactive loop is driven normally to provide reactive support for the power grid. At this time, the parallel box needs to reset the active power loop, that is, set the output value of the active power loop to zero. Specifically, before the output value of the active power loop of the parallel box is controlled to be zero, the total active power set value, output value and integral value of the PI controller of the active power loop of the parallel box before clearing are retained; at the same time, the reactive power loop of the parallel box is controlled to operate normally. Similarly, the converter side also needs to reset its own active power loop, that is, control the output value of the power loop of the converter to zero, and after receiving the reset instruction, if the converter does not detect a power grid fault within the preset time, the output value of its active power loop is controlled to be zero, and the active power set value, output value and integral value of the PI controller of its active power loop before clearing are retained; at the same time, the reactive power loop of the converter is controlled to operate normally. In this way, the multi-machine parallel converter system can also provide reactive power support for the power grid during high and low voltage crossing. At the same time, after the high and low voltage crossing is completed, the parallel box and the converter continue to operate with the parameters of the corresponding power loop before the high and low voltage crossing, thereby quickly recovering to the state before the crossing.

[0052] In a possible implementation manner, the implementation process of sending a reset instruction to each converter in S102, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected, includes:

[0053] A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output value of the corresponding active power loop when the reset instruction is detected and no grid fault is detected, and to save the power set value, output value and integral value of the active power loop before clearing.

[0054] In this embodiment, if the converter does not detect a grid fault within a preset period before and after detecting a reset instruction, the corresponding active power loop is controlled to reset, that is, the output value of the active power loop is controlled to be zero, but the power set value, output value and integral value of the active power loop before being reset are retained. At the same time, the converter controls its reactive power loop to maintain normal operation and provide reactive support for the grid.

[0055] In a possible implementation manner, if the condition in S102 is satisfied, the specific implementation process of controlling the power loop reset of the parallel box includes:

[0056] If the high and low voltage ride-through conditions are met, the output values ​​of the active power loop and the reactive power loop of the parallel box are cleared, and the power set value, output value and integral value of the active power loop and the reactive power loop before clearing are saved.

[0057] In this embodiment, as another international standard for high and low voltage crossing, when high and low voltage abnormalities occur in the power grid, it is necessary to reset the active loop and reactive loop of the converter, that is, control the converter to enter the pulse sealing mode. At this time, the parallel box needs to execute the reset logic for both the active power loop and the reactive power loop. Specifically, when the active power loop of the parallel box is reset, the output value of the active power loop of the parallel box is controlled to be zero, but the total active power set value, output value and integral value of the PI controller of the active power loop of the parallel box before clearing are saved. When the reactive power loop of the parallel box is reset, the output value of the reactive power loop of the parallel box is controlled to be zero, but the total reactive power set value, output value and integral value of the PI controller of the reactive power loop of the parallel box before clearing are saved. Similarly, the converter side also needs to reset its own active power loop and reactive power loop. Specifically, after receiving the reset command, if the converter does not detect a grid fault within the preset time, the output value of the corresponding active power loop is controlled to be zero, and the active power set value, output value, and integral value of the PI controller of the corresponding active power loop before clearing are saved. At the same time, when the converter controls the reactive power loop to reset, the output value of the corresponding reactive power loop is controlled to be zero, and the reactive power set value, output value, and integral value of the PI controller of the reactive power loop before clearing are saved. In this way, after the high and low voltage crossing is completed, the converter multi-machine parallel system can quickly recover to the state before crossing based on the parameters in the saved control loop.

[0058] In a possible implementation manner, in S102, a reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected. The specific implementation process includes:

[0059] A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output values ​​of the corresponding active power loop and reactive power loop when the reset instruction is detected and no power grid fault is detected, and to save the power set value, output value and integral value of the active power loop and the reactive power loop before clearing.

[0060] In this embodiment, if the converter does not detect a grid fault within a preset period before and after detecting a reset instruction, the output values ​​of the corresponding active power loop and reactive power loop are controlled to be zero, but the power set value, output value and integral value of the active power loop and the reactive power loop before clearing are saved.

[0061] Specifically, power grid faults include power grid overvoltage protection, power grid undervoltage protection, power grid overfrequency protection and power grid underfrequency protection.

[0062] In a possible implementation manner, the method provided in this embodiment further includes:

[0063] The power grid faults include power grid overvoltage protection and power grid undervoltage protection;

[0064] Before acquiring the grid electrical signal and determining whether the high and low voltage ride-through conditions are met according to the grid electrical signal, the method provided in this embodiment further includes:

[0065] Detect high and low voltage ride-through enable signals, and send a first control instruction to each converter when the high and low voltage ride-through enable signals are monitored; the first control instruction is used to indicate that the grid undervoltage protection threshold of each converter is less than the low voltage ride-through threshold, and the grid overvoltage protection threshold is greater than the high voltage ride-through threshold; the grid undervoltage protection threshold is used to determine whether the grid has grid undervoltage protection, and the grid overvoltage protection threshold is used to determine whether the grid has grid overvoltage protection.

[0066] In this embodiment, when the parallel box detects the high and low voltage ride through enable signal, it controls the converter to relax its grid fault monitoring threshold to avoid the situation where the converter is protected due to detecting grid faults during the high and low voltage ride through process.

[0067] Specifically, since the high and low voltage ride through monitoring is detected after the voltage of the grid electrical signal exceeds a certain threshold, the grid undervoltage and grid overvoltage faults are also detected after the voltage of the grid electrical signal exceeds a certain threshold. In order to avoid the converter detecting a grid fault due to high and low voltage ride through during the high and low voltage ride through process, resulting in the failure of high and low voltage ride through, in this embodiment, when the parallel box does not detect the high and low voltage ride through enable signal, the grid undervoltage protection threshold in the converter is set to a first value, for example, 85% U N ; The grid overvoltage protection threshold is a third value, for example, 115% U N ; When the parallel box detects the high and low voltage crossing enable signal, the grid undervoltage protection threshold in the converter is set to a second value, which is smaller than the first value, for example, the second value is 60%; the grid overvoltage protection threshold in the converter is set to a fourth value, which is greater than the third value, for example, the fourth value is 135%, to ensure the smooth execution of high and low voltage crossing.

[0068] From the above embodiments, it can be seen that the high and low voltage ride-through control method of the converter multi-machine parallel system provided in this embodiment can effectively solve the problems of inconsistent high and low voltage ride-through detection of the parallel converter, abnormal high and low voltage ride-through of the parallel system, and erroneous detection of high and low voltage abnormalities due to abnormal power detection of some converters, and meet the requirements of international standards for the high and low voltage ride-through capability of the converter multi-machine parallel system. In addition, this solution is simple and reliable, and can be directly applied to the existing converter multi-machine parallel system without excessive modification of the converter, and has scalability.

[0069] It should be understood that the order of execution of the steps in the above embodiment does not necessarily mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the present invention.

[0070] The following is an embodiment of the device of the present invention. For details not described in detail therein, reference may be made to the corresponding method embodiment described above.

[0071] Figure 3 The structure diagram of the high and low voltage ride through control device of the converter multi-machine parallel system provided by the embodiment of the present invention is shown. For the convenience of description, only the part related to the embodiment of the present invention is shown, which is described in detail as follows:

[0072] like Figure 3 As shown, the high and low voltage ride through control device 100 of the converter multi-machine parallel system includes:

[0073] The high and low voltage ride-through monitoring module 110 is used to obtain a grid electrical signal in a grid-connected operation mode, and determine whether a high and low voltage ride-through condition is met according to the grid electrical signal;

[0074] The control module 120 is used to control the power loop of the parallel box to reset if the conditions are met; and send a reset instruction to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected.

[0075] In a possible implementation manner, if the control module 120 is satisfied, then controlling the power loop of the parallel box to be reset includes:

[0076] If the high and low voltage ride-through conditions are met, the output value of the active power loop of the parallel box is cleared, and the power set value, output value and integral value of the active power loop before clearing are saved.

[0077] In a possible implementation manner, the control module 120 sends a reset instruction to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected, including:

[0078] A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output value of the corresponding active power loop when the reset instruction is detected and no grid fault is detected, and to save the power set value, output value and integral value of the active power loop before clearing.

[0079] In a possible implementation manner, if the control module 120 is satisfied, then controlling the power loop of the parallel box to be reset includes:

[0080] If the high and low voltage ride-through conditions are met, the output values ​​of the active power loop and the reactive power loop of the parallel box are cleared, and the power set value, output value and integral value of the active power loop and the reactive power loop before clearing are saved.

[0081] In a possible implementation manner, the control module 120 sends a reset instruction to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected, including:

[0082] A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output values ​​of the corresponding active power loop and reactive power loop when the reset instruction is detected and no power grid fault is detected, and to save the power set value, output value and integral value of the active power loop and the reactive power loop before clearing.

[0083] In a possible implementation, the high and low voltage ride through monitoring module 110 includes:

[0084] Acquiring a voltage signal between the AC bus and the power grid as a first voltage signal;

[0085] Whether a high or low voltage ride-through condition is met is determined according to the first voltage signal.

[0086] In a possible implementation manner, the power grid fault includes power grid overvoltage protection and power grid undervoltage protection; the high and low voltage ride through control device 100 of the converter multi-machine parallel system further includes:

[0087] A threshold change module is used to detect high and low voltage ride-through enable signals, and when the high and low voltage ride-through enable signals are monitored, a first control instruction is sent to each converter; the first control instruction is used to indicate that the grid undervoltage protection threshold of each converter is less than the low voltage ride-through threshold, and the grid overvoltage protection threshold is greater than the high voltage ride-through threshold; the grid undervoltage protection threshold is used to determine whether the grid has grid undervoltage protection, and the grid overvoltage protection threshold is used to determine whether the grid has grid overvoltage protection.

[0088] From the above embodiments, it can be seen that the high and low voltage ride-through control device of the converter multi-machine parallel system provided in this embodiment can effectively solve the problems of inconsistent high and low voltage ride-through detection of the converters in parallel, abnormal high and low voltage ride-through of the parallel system, and erroneous detection of high and low voltage abnormalities due to abnormal power detection of some converters, and meet the requirements of international standards for the high and low voltage ride-through capability of the converter multi-machine parallel system. In addition, this solution is simple and reliable, and can be directly applied to the existing converter multi-machine parallel system without excessive modification of the converter, and has scalability.

[0089] Figure 4 FIG. 1 is a schematic diagram of a parallel box provided by an embodiment of the present invention. Figure 4 As shown, the parallel box 4 of this embodiment includes: a processor 40 and a memory 41. The memory 41 is used to store a computer program 42, and the processor 40 is used to call and run the computer program 42 stored in the memory 41 to execute the steps in the above-mentioned high and low voltage ride-through control method embodiments of each converter multi-machine parallel system, such as Figure 2 Alternatively, the processor 40 is used to call and run the computer program 42 stored in the memory 41 to implement the functions of each module in the above-mentioned device embodiments, for example Figure 3 The functions of the modules 110 to 120 are shown.

[0090] Exemplarily, the computer program 42 may be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to implement the present invention. The one or more modules / units may be a series of computer program instruction segments capable of implementing specific functions, which are used to describe the execution process of the computer program 42 in the parallel box 4.

[0091] The parallel box 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will appreciate that Figure 4 It is only an example of the parallel box 4 and does not constitute a limitation of the parallel box 4. It may include more or less components than shown in the figure, or a combination of certain components, or different components. For example, the parallel box may also include input and output devices, network access devices, buses, etc.

[0092] The processor 40 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0093] The memory 41 may be an internal storage unit of the parallel box 4, such as a hard disk or memory of the parallel box 4. The memory 41 may also be an external storage device of the parallel box 4, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the parallel box 4. Further, the memory 41 may also include both an internal storage unit and an external storage device of the parallel box 4. The memory 41 is used to store the computer program and other programs and data required by the parallel box. The memory 41 may also be used to temporarily store data that has been output or is to be output.

[0094] The technicians in the relevant field can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0095] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0096] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0097] In the embodiments provided by the present invention, it should be understood that the disclosed device / parallel box and method can be implemented in other ways. For example, the device / parallel box embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0098] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0099] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0100] If the integrated module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the high and low voltage ride-through control method embodiments of each converter multi-machine parallel system can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device that can carry the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practices in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practices, computer-readable media does not include electrical carrier signals and telecommunication signals.

[0101] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A high and low voltage ride through control method for a multi-machine parallel converter system, characterized in that: The converter multi-machine parallel system comprises a parallel box and a plurality of converters; the parallel box comprises an AC bus, the AC side of each converter is connected to the AC bus, and the AC bus is used to connect to the power grid, and the parallel box is communicatively connected to each converter; The method is applied to the parallel box, comprising: In the grid-connected operation mode, a grid electrical signal is obtained, and whether a high or low voltage ride-through condition is met according to the grid electrical signal; If satisfied, the power loop of the parallel box is controlled to be reset; and a reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to reset the corresponding power loop when the reset instruction is detected and no grid fault is detected.

2. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 1, characterized in that: If the above conditions are met, the power loop of the parallel box is controlled to be reset, including: If the high and low voltage ride-through conditions are met, the output value of the active power loop of the parallel box is cleared, and the power set value, output value and integral value of the active power loop before clearing are saved.

3. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 2, characterized in that: The sending of a reset instruction to each converter, wherein the reset instruction is used to instruct each converter to reset a corresponding power loop when the reset instruction is detected and no power grid fault is detected, includes: A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output value of the corresponding active power loop when the reset instruction is detected and no grid fault is detected, and to save the power set value, output value and integral value of the active power loop before clearing.

4. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 1, characterized in that: If the above conditions are met, the power loop of the parallel box is controlled to be reset, including: If the high and low voltage ride-through conditions are met, the output values ​​of the active power loop and the reactive power loop of the parallel box are cleared, and the power set value, output value and integral value of the active power loop and the reactive power loop before clearing are saved.

5. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 4, characterized in that: The sending of a reset instruction to each converter, wherein the reset instruction is used to instruct each converter to reset a corresponding power loop when the reset instruction is detected and no power grid fault is detected, includes: A reset instruction is sent to each converter, wherein the reset instruction is used to instruct each converter to clear the output values ​​of the corresponding active power loop and reactive power loop when the reset instruction is detected and no power grid fault is detected, and to save the power set value, output value and integral value of the active power loop and the reactive power loop before clearing.

6. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 1, characterized in that: The method further comprises: Obtaining a power grid electrical signal, and determining whether a high or low voltage ride-through condition is met according to the power grid electrical signal, including: Acquiring a voltage signal between the AC bus and the power grid as a first voltage signal; Whether a high or low voltage ride-through condition is met is determined according to the first voltage signal.

7. The high and low voltage ride through control method of a converter multi-machine parallel system according to claim 1, characterized in that: The power grid faults include power grid overvoltage protection and power grid undervoltage protection; The control method further comprises: Detect high and low voltage ride-through enable signals, and send a first control instruction to each converter when the high and low voltage ride-through enable signals are monitored; the first control instruction is used to indicate that the grid undervoltage protection threshold of each converter is less than the low voltage ride-through threshold, and the grid overvoltage protection threshold is greater than the high voltage ride-through threshold; the grid undervoltage protection threshold is used to determine whether the grid has grid undervoltage protection, and the grid overvoltage protection threshold is used to determine whether the grid has grid overvoltage protection.

8. A parallel box, characterized in that: It includes an AC bus, a first switch, a second switch and a controller, wherein the AC bus is connected to the AC end of each converter respectively, the first end of the first switch and the first end of the second switch are both connected to the AC bus, the second end of the first switch is used to connect to the power grid, and the second end of the second switch is used to connect to the load; The controller is used to execute the high and low voltage ride through control method for a converter multi-machine parallel system according to any one of claims 1 to 7.

9. A converter multi-machine parallel system, characterized in that: The invention comprises a plurality of converters and a parallel box as claimed in claim 8.

10. The converter multi-machine parallel system according to claim 9, characterized in that: The converter is used for: When the reset instruction is detected and no power grid fault is detected, a power loop reset is performed.

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