Diode rectification sending system of new energy, direct current fault ride through method and device

Abstract

The application relates to the technical field of direct current transmission and discloses a diode rectifier sending-out system of new energy, a direct current fault crossing method and device, the system comprising a receiving end and a sending end connected through a direct current line; the receiving end comprising a first modular multi-level converter; the sending end comprising a diode rectifier and a second modular multi-level converter connected in series, the diode rectifier and the second modular multi-level converter being connected with an alternating current bus of a new energy power generation system; the first modular multi-level converter and the second modular multi-level converter both adopting a modular multi-level converter mixed with full-bridge submodules and half-bridge submodules, the control mode of the first modular multi-level converter comprising a constant direct current voltage / reactive current control mode and a zero current control mode, and the control mode of the second modular multi-level converter comprising a constant alternating current voltage / frequency control mode and a zero current control mode; and the application does not need to be additionally provided with a direct current circuit breaker and can reduce power transmission cost.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, specifically to a new energy diode rectification and transmission system, a DC fault ride-through method and apparatus. Background Technology

[0002] Currently, isolated renewable energy transmission projects often employ flexible DC converters based on Modular Multilevel Converters (MMCs). While more economical diode rectifiers can also be configured at DC receiving-end converter stations, renewable energy diode rectifier transmission systems struggle to overcome DC line faults. Firstly, diode rectifiers cannot automatically clear DC short-circuit currents; they must wait for the short-circuit current to decay and deionize before manually performing a black start, a time-consuming process. Secondly, diode rectifiers are uncontrolled rectifiers, unable to support grid connection of renewable energy and requiring grid-connected renewable energy units or auxiliary MMCs for self-starting. This characteristic makes it difficult for the system to recover automatically after a fault.

[0003] Current DC line fault ride-through technology is limited to traditional MMC type flexible DC, which uses the addition of DC circuit breakers. Its application is similar to that of AC circuit breakers and is a general fault clearing measure. It clears the short-circuit current by turning off the DC circuit breaker. However, DC circuit breaker technology is not yet mature and is expensive, which increases costs. Summary of the Invention

[0004] In view of this, the present invention provides a new energy diode rectification and transmission system, a DC fault ride-through method and apparatus, to solve the technical problem that the existing DC line fault ride-through method relies on the DC circuit breaker to turn off the short-circuit current, resulting in high costs.

[0005] In a first aspect, the present invention provides a diode rectification and output system for a new energy source, comprising a receiving end and a sending end connected by a DC line;

[0006] The receiving end includes a first modular multilevel converter;

[0007] The sending end includes a series-connected diode rectifier and a second modular multilevel converter, both of which are connected to the AC bus of the new energy power generation system.

[0008] Both the first and second modular multilevel converters adopt a hybrid modular multilevel converter consisting of full-bridge and half-bridge sub-modules. The control modes of the first modular multilevel converter include constant DC voltage / reactive current control mode and zero current control mode, while the control modes of the second modular multilevel converter include constant AC voltage / frequency control mode and zero current control mode.

[0009] In some alternative implementations, the diode rectifier output system for new energy sources also includes an AC energy dissipation device, which comprises several sets of energy dissipation units, any set of energy dissipation units being connected to the AC bus via a corresponding switching switch.

[0010] In a second aspect, the present invention provides a DC fault ride-through method, applied to controlling a diode rectifier power output system for a new energy source as described in any of the first aspects of the present invention, comprising:

[0011] Check for faults in the DC line;

[0012] If a DC line fault occurs, the first modular multilevel converter is locked out or the capacitors of all full-bridge sub-modules in the first modular multilevel converter are reverse-connected, and the control mode of the first modular multilevel converter is switched from constant DC voltage / reactive current control mode to zero current control mode.

[0013] Controlling the second modular multilevel converter to lock out or controlling the reverse connection of the capacitors of all full-bridge sub-modules in the second modular multilevel converter switches the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

[0014] In some alternative implementations, controlling the latch-up of the first modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the first modular multilevel converter includes:

[0015] The first real-time arm current of the first modular multilevel converter is detected. If the first real-time arm current is greater than the first blocking threshold, the first modular multilevel converter is controlled to be blocked. If the first real-time arm current is less than or equal to the first blocking threshold, the capacitors of all full-bridge sub-modules in the first modular multilevel converter are controlled to be connected in reverse.

[0016] Controlling the latch-up of the second modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the second modular multilevel converter includes:

[0017] The second real-time bridge arm current of the second modular multilevel converter is detected. If the second real-time bridge arm current is greater than the second blocking threshold, the second modular multilevel converter is controlled to be blocked. If the second real-time bridge arm current is less than or equal to the second blocking threshold, the capacitors of all full-bridge sub-modules in the second modular multilevel converter are controlled to be connected in reverse.

[0018] In some alternative implementations, after switching the control mode of the second modular multilevel converter from a constant AC voltage / frequency control mode to a zero current control mode, the method further includes:

[0019] The number of activated groups is determined based on the active power transmitted by DC before the fault, and the number of energy-consuming units connected to the AC bus in the AC energy-consuming device is controlled based on the number of activated groups.

[0020] At each sampling interval, the effective value of the AC voltage on the AC bus is detected, and the number of input groups is updated based on the effective value of the AC voltage. If the effective value of the AC voltage is higher than the voltage threshold, the number of input groups is increased; if the effective value of the AC voltage is lower than the voltage threshold, the number of input groups is decreased. The number of energy-consuming units in the AC energy-consuming device that are input to the AC bus is controlled based on the updated number of input groups.

[0021] In some alternative implementations, after a DC line fault is detected, the method further includes:

[0022] Check if the fault in the DC line has disappeared;

[0023] If the fault in the DC line disappears and all the full-bridge sub-modules in the first and second modular multilevel converters are connected in reverse, the reverse connection ratio of the full-bridge sub-modules in the first modular multilevel converter is gradually reduced from 1 to 0 based on the first slope. The control mode of the first modular multilevel converter is switched from zero current control mode to constant DC voltage / reactive current control mode, and the receiving-end DC voltage is restored to the first rated value.

[0024] The reverse connection ratio of the capacitors in the full-bridge submodule of the second modular multilevel converter is gradually reduced from 1 to 0 based on the second slope. The control mode of the second modular multilevel converter is switched from zero current control mode to constant AC voltage / frequency control mode, and the AC voltage at the sending end is restored to the second rated value.

[0025] In some alternative implementations, after restoring the sending-end AC voltage to the second rated value, the method further includes:

[0026] At each sampling interval, several groups of energy-consuming units are disconnected from the AC bus until the DC power is restored to the active power generated by the new energy power generation system.

[0027] Thirdly, the present invention provides a DC fault ride-through device, comprising:

[0028] The fault detection module is used to detect whether a fault has occurred in the DC line.

[0029] The receiving-end fault handling module is used to control the first modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the first modular multilevel converter to be connected in reverse if a fault occurs in the DC line, and to switch the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode.

[0030] The sending-end fault handling module is used to control the second modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the second modular multilevel converter to be connected in reverse, and to switch the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

[0031] Fourthly, the present invention provides a computer device, comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the computer instructions to perform the DC fault ride-through method of the second aspect above or any corresponding embodiment thereof.

[0032] Fifthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to perform the DC fault ride-through method of the second aspect or any corresponding embodiment described above.

[0033] The present invention has the following beneficial effects:

[0034] This invention discloses a new energy diode rectification and transmission system. A first modular multilevel converter is installed at the receiving end, and a second modular multilevel converter, connected in series, is installed at the transmitting end. When a DC line fault is detected, the system controls the first modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the first modular multilevel converter to be reverse-connected, switching the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode. Similarly, the system controls the second modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the second modular multilevel converter to be reverse-connected, switching the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode. This achieves rapid clearance of short-circuit current on the transmitting end DC side, eliminating the need for a DC circuit breaker and reducing transmission costs. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the diode rectification and power transmission system for new energy in the relevant scheme;

[0037] Figure 2 This is a schematic diagram of the structure of a new energy diode rectification and transmission system according to an embodiment of the present invention;

[0038] Figure 3 This is the control logic diagram of the first modular multilevel converter according to an embodiment of the present invention;

[0039] Figure 4 This is the control logic diagram of the second modular multilevel converter according to an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the control strategy of the new energy diode rectification and output system according to an embodiment of the present invention;

[0041] Figure 6 This is a flowchart of the DC fault ride-through method according to an embodiment of the present invention;

[0042] Figure 7 This is a structural block diagram of the DC fault ride-through device according to an embodiment of the present invention;

[0043] Figure 8 This is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] like Figure 1 As shown, currently in the power transmission field, the sending system using diode rectifiers only includes diode rectifiers at the sending end, while the receiving end is equipped with a modular multilevel converter containing a half bridge sub-module (HBSM), which requires the addition of a DC circuit breaker to clear the DC short-circuit current.

[0046] The new energy diode rectification and transmission system of this invention has a modular multilevel converter with a combination of full bridge sub-modules (FBSM) and half bridge sub-modules connected in series in the DC path of the diode rectifier. The DC short-circuit current is cleared by the blocking or active negative voltage control of the full bridge sub-module.

[0047] The new energy diode rectification and transmission system of this invention is applicable to power transmission schemes that use diode rectifiers for power transmission.

[0048] like Figure 2 As shown, the new energy diode rectification and transmission system of this invention includes a receiving end and a transmitting end connected by a DC line.

[0049] The receiving end includes a first modular multilevel converter;

[0050] The sending end includes a diode rectifier and a second modular multilevel converter connected in series. Both the diode rectifier and the second modular multilevel converter are connected to the AC bus of the new energy power generation system.

[0051] Both the first and second modular multilevel converters adopt a hybrid modular multilevel converter consisting of full-bridge and half-bridge sub-modules. The control modes of the first modular multilevel converter include constant DC voltage / reactive current control mode and zero current control mode, while the control modes of the second modular multilevel converter include constant AC voltage / frequency control mode and zero current control mode.

[0052] Among them, the diode rectifier transmission system for new energy is used to transmit the electrical energy generated by the new energy power generation system to the AC power grid. The new energy power generation system specifically includes new energy power generation systems such as wind power and solar power.

[0053] Specifically, the first modular multilevel converter is configured with a hybrid topology of full-bridge and half-bridge submodules, and its structure is the same as that of the second modular multilevel converter. The first modular multilevel converter includes two control modes: a constant DC voltage / reactive current control mode and a zero-current control mode, such as... Figure 3 Marked ① and ②; d-axis current in the first mode. The reference value is DC voltage. Controller output, q-axis current The reference value is a constant. In the second mode, the reference values ​​for both the d-axis and q-axis currents are zero. The arm current protection setting of the first modular multilevel converter, i.e., the first blocking threshold, is... If this value is exceeded, all sub-modules of the bridge arm will be locked out; the current threshold value for the active negative voltage control of the first modular multilevel converter is... ,in If the value exceeds this limit, the active negative pressure control function will be triggered. Figure 3 middle U dcref This is the DC voltage reference value. i abc For the three-phase current on the AC side, v abc For the three-phase voltage on the AC side, m abc It is a three-phase modulated voltage signal. θ This is the reference angle for coordinate transformation.

[0054] The second modular multilevel converter is configured with a hybrid topology of full-bridge and half-bridge sub-modules, connected in series on the DC side of the diode rectifier. The second modular multilevel converter includes two control modes: a constant AC voltage / frequency control mode and a zero-current control mode. Figure 4 Marked ① and ②; d-axis current in the first mode. The reference value is the d-axis voltage. Controller output, q-axis current The reference value is the q-axis voltage. The controller output uses a preset power frequency cycle reference angle θ for coordinate transformation. In the second mode, the reference values ​​for both the d-axis and q-axis currents are zero, and the coordinate transformation reference angle θ is obtained through a phase-locked loop. The arm current protection setting of the second modular multilevel converter, i.e., the second blocking threshold, is... If this value is exceeded, all sub-modules of the bridge arm will be locked out; the current threshold value for the active negative voltage control of the second modular multilevel converter is... ,in If the value is exceeded, the active negative voltage control function is triggered. For example, the second modular multilevel converter is connected in series between two diode rectifiers. Each phase arm of the second modular multilevel converter includes several half-bridge sub-modules, one full-bridge sub-module, and one inductor connected in series. Figure 4 middle V ref This is the AC voltage reference value. i abc For the three-phase current on the AC side, v abc For the three-phase voltage on the AC side, m abc It is a three-phase modulated voltage signal.

[0055] The new energy diode rectification and transmission system of this invention includes a first modular multilevel converter at the receiving end and a second modular multilevel converter connected in series at the sending end. When a DC line fault is detected, the system controls the first modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the first modular multilevel converter to be connected in reverse, switching the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode. Similarly, the system controls the second modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the second modular multilevel converter to be connected in reverse, switching the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode. This achieves rapid clearance of short-circuit current on the DC side of the sending end, eliminating the need for a DC circuit breaker and reducing transmission costs.

[0056] In some embodiments, the diode rectification and output system for new energy sources further includes an AC energy dissipation device, which includes several sets of energy dissipation units, any set of energy dissipation units being connected to the AC bus via a corresponding switching switch.

[0057] Specifically, the energy-consuming unit includes several energy-consuming resistors, and the switching switch is a controllable switch. The number of energy-consuming units activated is controlled by controlling the opening and closing of the switching switch. The overall rated capacity of the AC energy-consuming device is not less than the rated capacity of the new energy diode rectifier output system.

[0058] When a DC line fault is detected, the initial number of energy-consuming units to be activated is determined based on the DC power before the fault. Subsequently, the number of energy-consuming units to be activated is adjusted at certain time intervals according to changes in the AC bus voltage. By switching the AC energy-consuming units on and off, the AC voltage at the sending end is maintained within a reasonable range, such as the typical value of 0.9 pu to 1.1 pu, so that the generator set can operate without disconnecting from the grid.

[0059] Furthermore, such as Figure 5 As shown, during the recovery phase after fault clearance, the actions of each part in the new energy diode rectifier power transmission system are as follows:

[0060] First, the first modular multilevel converter at the receiving end performs the following actions: reducing the reverse connection ratio of the full-bridge submodule from 1 to 0 at a first slope; when this ratio drops to 0, switching to constant DC voltage / reactive current control mode and restoring the DC voltage to the first rated value. Here, the first rated value is the rated value of the DC voltage, and the magnitude of the first slope can be set according to actual conditions.

[0061] Secondly, the second modular multilevel converter at the sending end performs the following actions: reducing the reverse connection ratio of the full-bridge submodule from 1 to 0 according to the second slope; when the ratio drops to 0, switching to constant AC voltage / frequency control mode and restoring the sending-end AC voltage to the second rated value. Here, the second rated value is the rated value of the sending-end AC voltage, and the second slope can be set according to actual conditions; its magnitude can be the same as or different from the first slope.

[0062] Finally, the AC power consumption device operates as follows: the AC power consumption device will shut down the power consumption units that are currently in operation one group at a time, according to a relatively longer time interval, every sampling cycle.

[0063] The present invention also provides an embodiment of a DC fault ride-through method. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0064] This embodiment provides a DC fault ride-through method, applied to control a diode rectifier power-out system for a new energy source as described in the above embodiments of the present invention. Figure 6 As shown, the DC fault ride-through method includes the following steps:

[0065] Step S101: Detect whether a fault has occurred in the DC line.

[0066] Among them, DC line faults mainly include short circuit faults. The fault is determined by detecting the current in the DC line. For example, a fault is determined when the current in the DC line is greater than the fault threshold.

[0067] In step S102, if a fault occurs in the DC line, the first modular multilevel converter is locked or the capacitors of all full-bridge sub-modules in the first modular multilevel converter are reverse-connected, and the control mode of the first modular multilevel converter is switched from constant DC voltage / reactive current control mode to zero current control mode.

[0068] Among them, controlling the latch-up of the first modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the first modular multilevel converter includes:

[0069] The first real-time arm current of the first modular multilevel converter is detected. If the first real-time arm current is greater than the first blocking threshold, the first modular multilevel converter is controlled to be blocked. If the first real-time arm current is less than or equal to the first blocking threshold, the capacitors of all full-bridge sub-modules in the first modular multilevel converter are controlled to be connected in reverse.

[0070] Step S103: Control the second modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the second modular multilevel converter to be connected in reverse, and switch the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

[0071] Among them, controlling the latch-up of the second modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the second modular multilevel converter includes:

[0072] The second real-time bridge arm current of the second modular multilevel converter is detected. If the second real-time bridge arm current is greater than the second blocking threshold, the second modular multilevel converter is controlled to be blocked. If the second real-time bridge arm current is less than or equal to the second blocking threshold, the capacitors of all full-bridge sub-modules in the second modular multilevel converter are controlled to be connected in reverse.

[0073] Specifically, the first modular multilevel converter adopts a constant DC voltage / reactive current control mode during normal operation, while the second modular multilevel converter adopts a constant AC voltage / frequency control mode during normal operation.

[0074] Upon detecting a fault in the DC line, the various components controlling the diode rectifier power output system of the new energy source perform the following actions:

[0075] The first modular multilevel converter at the receiving end performs the following actions: if the arm current reaches the blocking condition, that is, the first real-time arm current of the first modular multilevel converter is greater than the first blocking threshold, then blocking is implemented; if the blocking condition is not reached, active negative voltage control is used to reverse the connection of all full-bridge submodule capacitors, that is, the reverse connection ratio of the full-bridge submodule jumps from 0 to 1; the control mode is switched from constant DC voltage / reactive current mode to zero current mode.

[0076] The second modular multilevel converter at the sending end performs the following actions: if the arm current reaches the blocking condition, that is, the second real-time arm current of the second modular multilevel converter is greater than the second blocking threshold, then blocking is implemented; if the blocking condition is not reached, active negative voltage control is used to reverse the connection of all full-bridge submodule capacitors, that is, the reverse connection ratio of the full-bridge submodule jumps from 0 to 1; the control mode is switched from constant AC voltage / frequency mode to zero current mode.

[0077] The DC fault ride-through method of this invention, when a fault is detected in the DC line, controls the first modular multilevel converter to be locked or controls the capacitors of all full-bridge submodules in the first modular multilevel converter to be connected in reverse, switching the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode. Similarly, it controls the second modular multilevel converter to be locked or controls the capacitors of all full-bridge submodules in the second modular multilevel converter to be connected in reverse, switching the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode. This achieves rapid clearance of short-circuit current on the DC side of the sending end, eliminating the need for a DC circuit breaker and reducing transmission costs.

[0078] In some alternative implementations, after switching the control mode of the second modular multilevel converter from a constant AC voltage / frequency control mode to a zero current control mode in step S103, the method further includes:

[0079] Step S104: Determine the number of activated groups based on the active power transmitted by DC before the fault, and control the number of energy-consuming units in the AC energy-consuming device that are activated to the AC bus based on the number of activated groups.

[0080] Step S105: Every sampling period, detect the effective value of AC voltage on the AC bus, and update the number of input groups according to the effective value of AC voltage. If the effective value of AC voltage is higher than the voltage threshold, increase the number of input groups; if the effective value of AC voltage is lower than the voltage threshold, decrease the number of input groups. Control the number of energy-consuming units in the AC energy-consuming device that are input to the AC bus based on the updated number of input groups.

[0081] When a DC line fault is detected, the AC energy dissipation device operates as follows: Based on the active power transmitted via DC before the fault, the initial number of energy dissipation units activated is determined; subsequently, at certain time intervals (i.e., every sampling cycle), the number of activated energy dissipation units is adjusted according to changes in the AC bus voltage. By switching the AC energy dissipation device on and off, the sending-end AC voltage is maintained within a reasonable range, such as the typical value of 0.9 pu~1.1 pu, enabling the generator unit to operate without disconnecting from the grid.

[0082] The formula for calculating the number of energy-consuming units to be put into operation during a fault process is as follows:

[0083]

[0084]

[0085] In the formula, The number of input groups for energy-consuming units. The number of input groups before rounding. For the floor function, This represents the maximum number of energy-consuming units. The sampling period is For sampling sequence number, This represents the active power transmitted via DC before the fault. This refers to the rated power of a single energy-consuming unit. The slope coefficient of the number of input groups with respect to voltage deviation. This is the effective value of the AC voltage. Voltage threshold, The point in time when the fault was detected. This is the starting point for power recovery.

[0086] It should be understood that the number of power-consuming units in operation is 0 until a fault is detected.

[0087] After switching the control mode of the second modular multilevel converter to the zero-current control mode, the number of energy-consuming units of the AC energy-consuming device is determined according to the active power of DC transmission before the fault, and the number of units is dynamically updated based on the effective value of AC bus voltage. This can maintain the AC voltage within a reasonable range while absorbing the surplus power of new energy, so that new energy can maintain normal grid-connected power generation during DC faults and recovery phases, avoiding new energy disconnection from the grid and system shutdown.

[0088] In some embodiments, after a DC line fault is detected, the method further includes:

[0089] Step S201: Check whether the fault in the DC line has disappeared.

[0090] Step S202: If the fault in the DC line disappears and the capacitors of all full-bridge sub-modules in the first modular multilevel converter and the second modular multilevel converter are reverse connected, then the reverse connection ratio of the capacitors of the full-bridge sub-modules in the first modular multilevel converter is gradually reduced from 1 to 0 based on the first slope. The control mode of the first modular multilevel converter is switched from the zero current control mode to the constant DC voltage / reactive current control mode, and the receiving-end DC voltage is restored to the first rated value.

[0091] Step S203: The reverse connection ratio of the capacitors in the full-bridge submodule of the second modular multilevel converter is gradually reduced from 1 to 0 based on the second slope. The control mode of the second modular multilevel converter is switched from zero current control mode to constant AC voltage / frequency control mode, and the AC voltage at the sending end is restored to the second rated value.

[0092] Furthermore, in step S203, after restoring the AC voltage at the sending end to the second rated value, the method further includes:

[0093] In step S204, every time a sampling cycle is completed, several groups of energy-consuming units are disconnected from the AC bus until the DC power is restored to the active power generated by the new energy power generation system.

[0094] Specifically, when the current in the DC line is detected to be less than the fault threshold, the fault is determined to have disappeared, and the various parts of the new energy diode rectification and output system are controlled to perform the following actions:

[0095] First, the first modular multilevel converter at the receiving end performs the following actions: reducing the reverse connection ratio of the full-bridge submodule from 1 to 0 at a first slope; when this ratio drops to 0, switching to constant DC voltage / reactive current control mode and restoring the DC voltage to the first rated value. Here, the first rated value is the rated value of the DC voltage, and the magnitude of the first slope can be set according to actual conditions.

[0096] Secondly, the second modular multilevel converter at the sending end performs the following actions: reducing the reverse connection ratio of the full-bridge submodule from 1 to 0 according to the second slope; when the ratio drops to 0, switching to constant AC voltage / frequency control mode and restoring the sending-end AC voltage to the second rated value. Here, the second rated value is the rated value of the sending-end AC voltage, and the second slope can be set according to actual conditions; its magnitude can be the same as or different from the first slope.

[0097] Finally, the AC power dissipation device operates as follows: At relatively longer time intervals, it sequentially deactivates each group of power dissipation units currently in operation, every sampling cycle. The formula for calculating the number of power dissipation units in operation during the recovery process is as follows:

[0098]

[0099]

[0100] In the formula, The time of exit for each power-consuming unit and the sampling period during power recovery. The ratio of .

[0101] In the fault recovery phase of this invention, the first modular multilevel converter at the receiving end, the second modular multilevel converter at the sending end, and the AC energy dissipation device are sequentially switched in control state, which can realize the smooth and orderly recovery of DC voltage, AC voltage at the sending end, and new energy power.

[0102] Furthermore, two measures are taken to reduce transient impacts: first, the proportion of the full-bridge submodule capacitors connected in reverse decreases at a certain slope to prevent overcurrent in the bridge arm; second, the energy-consuming units in the AC energy-consuming device are disconnected one group at a certain time interval, so that the second modular multilevel converter at the sending end can control the AC voltage smoothly in stages and prevent voltage collapse.

[0103] This invention also provides a DC fault ride-through device, such as... Figure 7 As shown, it includes:

[0104] Fault detection module 101 is used to detect whether a fault has occurred in the DC line;

[0105] The receiving-end fault handling module 102 is used to control the first modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the first modular multilevel converter to be connected in reverse if a fault occurs in the DC line, and to switch the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode.

[0106] The sending-end fault handling module 103 is used to control the second modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the second modular multilevel converter to be connected in reverse, and to switch the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

[0107] The DC fault ride-through device of this invention, when a fault is detected in the DC line, controls the first modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the first modular multilevel converter to be connected in reverse, switching the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode. Similarly, it controls the second modular multilevel converter to lock out or controls the capacitors of all full-bridge submodules in the second modular multilevel converter to be connected in reverse, switching the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode. This achieves rapid clearance of short-circuit current on the DC side of the sending end, eliminating the need for a DC circuit breaker and reducing transmission costs.

[0108] Furthermore, the receiving-end fault handling module 102 is also used for:

[0109] The first real-time arm current of the first modular multilevel converter is detected. If the first real-time arm current is greater than the first blocking threshold, the first modular multilevel converter is controlled to be blocked. If the first real-time arm current is less than or equal to the first blocking threshold, the capacitors of all full-bridge sub-modules in the first modular multilevel converter are controlled to be connected in reverse.

[0110] The sending end fault handling module 103 is also used for:

[0111] The second real-time bridge arm current of the second modular multilevel converter is detected. If the second real-time bridge arm current is greater than the second blocking threshold, the second modular multilevel converter is controlled to be blocked. If the second real-time bridge arm current is less than or equal to the second blocking threshold, the capacitors of all full-bridge sub-modules in the second modular multilevel converter are controlled to be connected in reverse.

[0112] Furthermore, the DC fault ride-through device also includes:

[0113] The fault-phase energy consumption switching module is used to determine the number of switching groups based on the active power transmitted by DC before the fault, and to control the number of energy consumption units connected to the AC bus in the AC energy consumption device based on the number of switching groups. Every sampling period, the effective value of AC voltage on the AC bus is detected, and the number of switching groups is updated based on the effective value of AC voltage. If the effective value of AC voltage is higher than the voltage threshold, the number of switching groups is increased; if the effective value of AC voltage is lower than the voltage threshold, the number of switching groups is decreased. The number of energy consumption units connected to the AC bus in the AC energy consumption device is controlled based on the updated number of switching groups.

[0114] Furthermore, the DC fault ride-through device also includes:

[0115] The fault disappearance detection module is used to detect whether the fault in the DC line has disappeared;

[0116] The receiving-end recovery processing module is used to, if the fault of the DC line disappears and the capacitors of all full-bridge sub-modules in the first modular multilevel converter and the second modular multilevel converter are reverse connected, gradually reduce the reverse connection ratio of the capacitors of the full-bridge sub-modules in the first modular multilevel converter from 1 to 0 based on a first slope, switch the control mode of the first modular multilevel converter from zero current control mode to constant DC voltage / reactive current control mode, and restore the receiving-end DC voltage to the first rated value.

[0117] The sending-end recovery processing module is used to gradually reduce the reverse connection ratio of the capacitors of the full-bridge sub-module in the second modular multilevel converter from 1 to 0 based on the second slope, switch the control mode of the second modular multilevel converter from zero current control mode to constant AC voltage / frequency control mode, and restore the sending-end AC voltage to the second rated value.

[0118] Furthermore, the DC fault ride-through device also includes:

[0119] The recovery phase energy consumption switching module is used to disconnect several groups of energy consumption units from the AC bus at each sampling cycle until the DC power is restored to the active power generated by the new energy power generation system.

[0120] This invention also provides a schematic diagram of the structure of a computer device, such as... Figure 8As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 8 Take a processor 10 as an example.

[0121] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0122] The memory 20 stores instructions executable by at least one processor 10 to cause at least one processor 10 to perform the method shown in the above embodiments.

[0123] The memory 20 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the computer device. Furthermore, the memory 20 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some alternative embodiments, the memory 20 may optionally include memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0124] The memory 20 may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0125] The computer device also includes an input device 30 and an output device 40. The processor 10, memory 20, input device 30, and output device 40 can be connected via a bus or other means. Figure 8 Taking the example of a connection between China and Israel via a bus.

[0126] Input device 30 can receive input numerical or character information, and generate key signal inputs related to user settings and function control of the computer device, such as a touchscreen, keypad, mouse, trackpad, touchpad, joystick, one or more mouse buttons, trackball, joystick, etc. Output device 40 may include display devices, auxiliary lighting devices (e.g., LEDs), and haptic feedback devices (e.g., vibration motors). The aforementioned display devices include, but are not limited to, liquid crystal displays, light-emitting diodes, displays, and plasma displays. In some alternative embodiments, the display device may be a touchscreen.

[0127] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0128] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0129] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and all such modifications and variations fall within the scope of protection.

Claims

1. A DC fault ride-through method, characterized in that, A diode rectifier power transmission system for controlling new energy sources includes a receiving end and a sending end connected by a DC line. The receiving end includes a first modular multilevel converter (MMC). The sending end includes a diode rectifier and a second modular multilevel converter connected in series. Both the diode rectifier and the second modular multilevel converter are connected to the AC bus of the new energy power generation system. Both the first and second modular multilevel converters are modular multilevel converters using a hybrid of full-bridge and half-bridge sub-modules. The control modes of the first modular multilevel converter include a constant DC voltage / reactive current control mode and a zero-current control mode. The control modes of the second modular multilevel converter include a constant AC voltage / frequency control mode and a zero-current control mode. The new energy diode rectifier power transmission system also includes an AC energy consumption device, which includes several groups of energy consumption units. Each group of energy consumption units is connected to the AC bus through a corresponding switching switch. DC fault ride-through methods include: Check for faults in the DC line; If a DC line fault occurs, the first modular multilevel converter is locked or the capacitors of all full-bridge sub-modules in the first modular multilevel converter are reverse-connected, and the control mode of the first modular multilevel converter is switched from constant DC voltage / reactive current control mode to zero current control mode. Controlling the second modular multilevel converter to lock out or controlling the capacitors of all full-bridge sub-modules in the second modular multilevel converter to reverse the connection, switches the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

2. The DC fault ride-through method according to claim 1, characterized in that, Controlling the latching of the first modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the first modular multilevel converter includes: The first real-time arm current of the first modular multilevel converter is detected. If the first real-time arm current is greater than the first blocking threshold, the first modular multilevel converter is controlled to be blocked. If the first real-time arm current is less than or equal to the first blocking threshold, the capacitors of all full-bridge sub-modules in the first modular multilevel converter are controlled to be connected in reverse. Controlling the latch-up of the second modular multilevel converter or controlling the reverse connection of the capacitors of all full-bridge submodules in the second modular multilevel converter includes: The second real-time arm current of the second modular multilevel converter is detected. If the second real-time arm current is greater than the second blocking threshold, the second modular multilevel converter is controlled to be blocked. If the second real-time arm current is less than or equal to the second blocking threshold, the capacitors of all full-bridge sub-modules in the second modular multilevel converter are controlled to be connected in reverse.

3. The DC fault ride-through method according to claim 1, characterized in that, After switching the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode, the following steps are also included: The number of input groups is determined based on the active power transmitted by DC before the fault, and the number of energy-consuming units in the AC energy-consuming device that are input to the AC bus is controlled based on the number of input groups. At each sampling interval, the effective value of the AC voltage on the AC bus is detected, and the number of input groups is updated according to the effective value of the AC voltage. If the effective value of the AC voltage is higher than the voltage threshold, the number of input groups is increased; if the effective value of the AC voltage is lower than the voltage threshold, the number of input groups is decreased. The number of energy-consuming units in the AC energy-consuming device that are input to the AC bus is controlled based on the updated number of input groups.

4. The DC fault ride-through method according to claim 1, characterized in that, After a fault is detected in the DC line, the following is also included: Check if the fault in the DC line has disappeared; If the fault in the DC line disappears and all the capacitors of the full-bridge sub-modules in the first modular multilevel converter and the second modular multilevel converter are reverse connected, then the reverse connection ratio of the capacitors of the full-bridge sub-modules in the first modular multilevel converter is gradually reduced from 1 to 0 based on the first slope, the control mode of the first modular multilevel converter is switched from the zero current control mode to the constant DC voltage / reactive current control mode, and the receiving-end DC voltage is restored to the first rated value. The reverse connection ratio of the capacitor in the full-bridge submodule of the second modular multilevel converter is gradually reduced from 1 to 0 based on the second slope. The control mode of the second modular multilevel converter is switched from zero current control mode to constant AC voltage / frequency control mode, and the AC voltage at the sending end is restored to the second rated value.

5. The DC fault ride-through method according to claim 4, characterized in that, After restoring the AC voltage at the sending end to the second rated value, the process also includes: At each sampling interval, several groups of energy-consuming units are disconnected from the AC bus until the DC power is restored to the active power generated by the new energy power generation system.

6. A DC fault ride-through device, characterized in that, A diode rectifier power transmission system for controlling new energy sources includes a receiving end and a sending end connected by a DC line. The receiving end includes a first modular multilevel converter (MMC). The sending end includes a diode rectifier and a second modular multilevel converter connected in series. Both the diode rectifier and the second modular multilevel converter are connected to the AC bus of the new energy power generation system. Both the first and second modular multilevel converters are modular multilevel converters using a hybrid of full-bridge and half-bridge sub-modules. The control modes of the first modular multilevel converter include a constant DC voltage / reactive current control mode and a zero-current control mode. The control modes of the second modular multilevel converter include a constant AC voltage / frequency control mode and a zero-current control mode. The new energy diode rectifier power transmission system also includes an AC energy consumption device, which includes several groups of energy consumption units. Each group of energy consumption units is connected to the AC bus through a corresponding switching switch. DC fault ride-through devices include: The fault detection module is used to detect whether a fault has occurred in the DC line. The receiving-end fault handling module is used to control the first modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the first modular multilevel converter to be connected in reverse if a fault occurs in the DC line, and to switch the control mode of the first modular multilevel converter from constant DC voltage / reactive current control mode to zero current control mode. The sending-end fault handling module is used to control the second modular multilevel converter to lock out or control the capacitors of all full-bridge sub-modules in the second modular multilevel converter to be connected in reverse, and to switch the control mode of the second modular multilevel converter from constant AC voltage / frequency control mode to zero current control mode.

7. A computer device, characterized in that, include: A memory and a processor are communicatively connected, the memory storing computer instructions, and the processor executing the computer instructions to perform the DC fault ride-through method according to any one of claims 1 to 5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to perform the DC fault ride-through method according to any one of claims 1 to 5.

Images