Tandem direct current voltage regulation method, device and system based on double-loop architecture

Abstract

The invention discloses a series connection type direct current voltage regulation method, device and system based on a double-loop framework, and belongs to the technical field of power electronics, and the method comprises the steps: setting the switching state of a direct current loop according to the size of a tail end load of a power transmission line; the direct-current loop comprises a first direct-current loop and a second direct-current loop; setting a switching state of a direct current voltage regulating device according to the equipment fault condition on the direct current loop; the direct current voltage regulating device comprises a first direct current voltage regulating device and a second direct current voltage regulating device; and regulating and controlling the magnitude and the direction of the current in the direct current voltage regulating device and the direct current loop which are in a connected state based on a comparison result of the tail end voltage of the power transmission line and a preset voltage normal range. The problems that in the prior art, a direct-current voltage regulating device is only suitable for the working conditions that the power transmission distance between the head end and the tail end is not long and the head end voltage is normal, and the compensation capacity of the tail end parallel connection mode for the tail end unbalanced voltage is limited can be solved.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and specifically relates to a series direct current voltage regulation method and system based on a dual-circuit architecture. Background Art

[0002] As the terminal link of the power system, the low-voltage distribution network directly faces the vast number of users. It is the cornerstone for ensuring the transmission of electricity to thousands of households and supporting the normal operation of social production and life. It plays an indispensable basic supporting role in economic development and social stability. Due to the wide power supply range of the low-voltage distribution network and the high voltage drop in long lines, the voltage of the end users is low. When a large number of loads pour in during peak hours, the voltage drop will be further aggravated. In addition, when the peak-to-valley difference of the load is large, frequent voltage fluctuations will occur, which not only affects the service life and performance of the electrical equipment, but also poses a threat to the stable operation of the power system. In addition, if the reactive power compensation is insufficient during the operation of the inductive load, it is very easy to cause the voltage quality to deteriorate and the voltage level to decrease.

[0003] At present, parallel DC voltage regulators based on power electronic converters are commonly used for substation voltage management. Among them, the rectifier and inverter of the parallel DC voltage regulator are connected in parallel at the head end and the end end (load side) of the substation respectively. When the low voltage or high voltage at the end is detected, the device will start the low / high voltage management mode. Usually, the inverter at the end operates in the current source mode, and the rectifier at the head end operates in the voltage source mode. When the voltage at the end is normal, the device operates in the energy-saving mode. However, the parallel DC voltage regulator is only suitable for the working conditions where the power transmission distance between the head and the end is not too far and the voltage at the head end is normal. In addition, the parallel connection method at the end has limited compensation ability for the unbalanced voltage at the end. Therefore, how to effectively manage the high and low voltage problems caused by long-distance power transmission in remote mountainous areas, rural areas and other areas is the main research issue at present. Summary of the invention

[0004] The present application proposes a series DC voltage regulation method, device and system based on a dual-circuit architecture, which can solve the problem that the DC voltage regulation device in the prior art is only suitable for the working conditions where the power transmission distance between the head and the terminal is not too far and the voltage at the head end is normal, and the terminal parallel connection method has limited compensation ability for the unbalanced voltage at the terminal.

[0005] A first aspect of the present application provides a series DC voltage regulation method based on a dual-loop architecture, the method comprising:

[0006] According to the end load size of the transmission line, the switching state of the DC circuit is set; wherein the DC circuit includes a first DC circuit and a second DC circuit, and the DC circuit is a transmission line connecting the internal modules of the DC voltage regulator;

[0007] Set the switching state of the DC voltage regulating device according to the equipment fault conditions on the DC circuit; wherein, the DC voltage regulating device includes a first DC voltage regulating device and a second DC voltage regulating device; the first DC voltage regulating device is connected in series on the first DC circuit, and the second DC voltage regulating device is connected in series on the second DC circuit;

[0008] Based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, regulate the magnitude and direction of the current in the DC voltage regulating device and the DC circuit in the connected state to regulate the terminal voltage.

[0009] The above solution sets a series-type DC voltage regulating topology on the transmission line, including two DC voltage regulating devices and two DC circuits. Each DC circuit is connected in series with a DC voltage regulating device. The rectifier module of the DC voltage regulating device is connected to the transformer outlet side of the transmission line, and the inverter module is connected to the terminal load side of the transmission line to achieve terminal voltage governance through the DC voltage regulating device. Determine how many DC circuits are required to participate in voltage governance according to the terminal load size, reasonably plan the operation time of the DC circuits, and meet the power demand as quickly as possible, avoiding the influence of a single circuit on its service life due to excessive operation time. In addition, determine which device is used for voltage regulation according to the number of faults in the DC voltage regulating device, bypass the voltage regulating device with too many faults and perform power-off maintenance, and put the voltage regulating device with no faults or very few faults into operation, so as to ensure the normal operation of the DC circuit and maintain normal power supply at the remote end even in case of faults. Finally, for the situation of too low or too high terminal voltage, adjust the control signal sequence and PWM duty cycle of the power switch device to regulate the magnitude and direction of the current in the DC voltage regulating device and the DC circuit, so as to change the magnitude of the output current, thereby affecting the magnitude of the terminal voltage, so that the terminal voltage is maintained within a stable range, achieving precise governance of the terminal voltage and maintaining the operation stability of the power system.

[0010] In a possible implementation method of the first aspect, set the switching state of the DC circuit according to the terminal load size of the transmission line, specifically:

[0011] Real-time collect the terminal load size to determine whether the current transmission line is in a preset full-power operation condition or a preset non-full-power operation condition;

[0012] If it is the non-full-power operation condition, set the first DC circuit and the second DC circuit to alternately enter the connected state;

[0013] If it is the full-power operation condition, set both the first DC circuit and the second DC circuit to the connected state.

[0014] The above solution divides the load size into full-power operation conditions and non-full-power operation conditions. Under non-full-power operation conditions, the end load is small. Therefore, alternating the operation of the two DC circuits can reduce the circuit operation time while regulating the voltage, extend the service life of the equipment, and reduce the equipment usage cost. Under full-power operation conditions, the end load is large. Therefore, both DC circuits need to be put into operation to complete voltage regulation more quickly and ensure sufficient power supply to end users.

[0015] In a possible implementation method of the first aspect, the first DC circuit and the second DC circuit are set to alternately enter the connected state, specifically:

[0016] When one of the first DC circuit and the second DC circuit is set to the connected state, the other circuit is set to the disconnected state;

[0017] When the total duration of being set to the connected state exceeds the first operation time, the DC circuit in the connected state is switched to the disconnected state.

[0018] In a possible implementation method of the first aspect, it further includes:

[0019] According to the comparison result of the end load size and a preset first threshold, determine the number of rectifier modules and inverter modules participating in voltage regulation in the DC voltage regulating device; wherein, the rectifier modules and inverter modules are based on a T-type three-level three-phase four-leg topology.

[0020] Among them, the greater the end load size is than the first threshold, the more rectifier modules and inverter modules participating in voltage regulation in the DC voltage regulating device.

[0021] In a possible implementation method of the first aspect, according to the equipment fault situation on the DC circuit, set the switching state of the DC voltage regulating device, specifically:

[0022] Detect the equipment fault situation on the DC circuit and record the number of fault locations in the DC voltage regulating device;

[0023] If there is only one fault location on any of the DC voltage regulating devices, bypass the fault location and the DC voltage regulating device continues to operate;

[0024] If there are multiple fault locations in any of the DC voltage regulating devices, bypass the DC circuit corresponding to the DC voltage regulating device with a fault and put the other DC circuit into operation;

[0025] If there are multiple fault locations in all of the DC voltage regulating devices, bypass all of the DC voltage regulating devices and switch the DC circuit to AC power transmission.

[0026] The above solution determines whether the voltage regulating device and the corresponding DC circuit can be connected to the line for voltage regulation by detecting the number of fault points in the DC voltage regulating device, so as to ensure that the voltage regulation can be normally executed and ensure that the remote end can always be normally powered. When there is only one fault in the DC voltage regulating device, only the fault point is not connected to the DC circuit; when there are more faults in the DC voltage regulating device, the DC circuit where the DC voltage regulating device is located is bypassed for power-off maintenance, and another normal operating DC circuit is used for voltage regulation; when all voltage regulating devices have faults, the transmission line is directly changed to AC transmission, and then changed back to DC transmission for voltage regulation again after the maintenance is completed, realizing the efficient and stable operation of the distribution network system.

[0027] In a possible implementation method of the first aspect, it further includes:

[0028] After completing the bypass operation, perform power-off maintenance on the DC voltage regulating device with fault points, and then put the DC voltage regulating device after the maintenance back into operation by operating the bypass switch.

[0029] In the above solution, during the voltage regulation process, the faulty DC voltage regulating device is bypassed for power-off maintenance, and the DC voltage regulating device is put back into operation until the fault is eliminated, so as to realize the replacement of the faulty DC circuit. Moreover, silicon carbide materials are also used to make power switch devices, enabling the power switch devices to have better high-temperature stability and still maintain good stability and reliability under high-frequency and high-voltage conditions, avoiding adverse situations such as excessive switching loss, thermal runaway, and avalanche breakdown, and further improving the overall performance of the device.

[0030] In a possible implementation method of the first aspect, based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, the magnitudes and directions of the currents in the connected DC voltage regulating device and the DC circuit are regulated. Specifically:

[0031] The terminal voltage is collected in real time and compared with the normal voltage range.

[0032] When the terminal voltage is greater than the normal voltage range, the connected DC voltage regulating device is set to the high-voltage governance mode.

[0033] When the terminal voltage is less than the normal voltage range, the connected DC voltage regulating device is set to the low-voltage governance mode.

[0034] In a possible implementation method of the first aspect, the high-voltage governance mode and the low-voltage governance mode are specifically:

[0035] In the high-voltage governance mode, by adjusting the control signal sequence of the power switching device, the current direction of the inverter module in the DC voltage regulating device is changed to be from the AC side to the DC side, and then by adjusting the PWM duty cycle of the switching device in the inverter module, the output current magnitude of the DC voltage regulating device is adjusted to reduce the terminal voltage.

[0036] In the low-voltage governance mode, by increasing the PWM duty cycle of the switching device in the inverter module of the DC voltage regulating device, the output current magnitude of the DC voltage regulating device is adjusted to increase the terminal voltage.

[0037] The above solution manages the terminal low voltage and high voltage through the DC voltage regulating device and the DC circuit. When managing high voltage, by changing the current direction within the series-type DC voltage regulating topology and adjusting the magnitude of the output current, the terminal voltage is reduced to return to the normal voltage range; when managing low voltage, by increasing the magnitude of the output current to compensate for the reduction in the terminal voltage, the terminal equipment can receive sufficient voltage to maintain normal operation and provide sufficient power for the terminal users.

[0038] The second aspect of this application provides a series-type DC voltage regulating device based on a dual-loop architecture. The system includes: a loop setting module, a voltage regulating device setting module, and a voltage regulating module.

[0039] Among them, the loop setting module is used to set the switching state of the DC loop according to the magnitude of the terminal load of the transmission line. Among them, the DC loop includes a first DC loop and a second DC loop, and the DC loop is a transmission line connecting the internal modules of the DC voltage regulating device.

[0040] The voltage regulating device setting module is used to set the switching state of the DC voltage regulating device according to the equipment fault condition on the DC loop. Among them, the DC voltage regulating device includes a first DC voltage regulating device and a second DC voltage regulating device; the first DC voltage regulating device is connected in series on the first DC loop, and the second DC voltage regulating device is connected in series on the second DC loop.

[0041] The voltage regulating module is used to regulate the magnitude and direction of the current in the connected DC voltage regulating device and the DC loop based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, so as to regulate the terminal voltage.

[0042] The third aspect of this application provides a series-type DC voltage regulating system based on a dual-loop architecture. The system includes: a series-type DC voltage regulating device and a series-type DC voltage regulating topology.

[0043] Among them, the series-type DC voltage regulating topology includes a first DC voltage regulating device, a first DC loop, a second DC voltage regulating device, and a second DC loop.

[0044] The first DC voltage regulating device includes a first rectifier main unit and a first inverter slave unit; the second DC voltage regulating device includes a second rectifier main unit and a second inverter slave unit; wherein, both the first rectifier main unit and the second rectifier main unit include a plurality of rectifier modules, and both the first inverter slave unit and the second inverter slave unit include a plurality of inverter modules;

[0045] The first rectifier main unit and the second rectifier main unit are respectively connected to the transformer outgoing side of the transmission line;

[0046] The first inverter slave unit and the second inverter slave unit are respectively connected to the end load side of the transmission line;

[0047] The series DC voltage regulating device is used to implement a series DC voltage regulating method based on a dual-loop architecture described in any one of the embodiments of the present application. Description of the Drawings

[0048] In order to more clearly illustrate the technical solutions of the present application, the drawings required for implementation will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0049] Figure 1 It is a specific flow schematic diagram of a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0050] Figure 2 It is the topological structure of a traditional dual-loop series voltage regulating device for a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0051] Figure 3 It is the topological structure of a traditional parallel voltage regulating device for a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0052] Figure 4 It is the topological structure of a dual-loop series voltage regulating device for a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0053] Figure 5 It is the dual-loop series DC voltage regulating topological structure of a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0054] Figure 6 It is the T-type three-level three-phase four-leg topological structure of a series DC voltage regulating method based on a dual-loop architecture provided by an embodiment of the present application;

[0055] Figure 7 It is the specific structure diagram of a series DC voltage regulating device based on a dual-loop architecture provided by an embodiment of the present application;

[0056] Figure 8 It is the specific structure diagram of a series DC voltage regulating system based on a dual-loop architecture provided by an embodiment of the present application. Specific implementation manners

[0057] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0058] It should be understood that the step numbers used in the text are only for convenience of description and are not intended to limit the order of execution of the steps.

[0059] The first embodiment

[0060] When high voltage or low voltage appears at the end of the transmission line, usually the inverter at the end operates in the current source mode, and the rectifier at the head end operates in the voltage source mode to adjust the end voltage to the normal voltage range. However, in remote mountainous areas, rural areas and other areas where long-distance power transmission is required, traditional shunt voltage regulating devices are difficult to effectively complete the voltage management at the head and end, and the compensation ability of the shunt connection method at the end for unbalanced voltage is also limited. Therefore, how to achieve long-distance voltage management with low cost and high reliability, improve the stability of the end grid voltage and the compensation depth for unbalanced voltage is the main research direction of the embodiments of the present application.

[0061] As Figure 1 shown, to solve the problem that the existing DC voltage regulating device in the prior art is only applicable to the working conditions where the power transmission distance between the head and end is not too far and the head-end voltage is normal, and the compensation ability of the shunt connection method at the end for the end unbalanced voltage is also limited, an embodiment of the present application provides a specific flow schematic diagram of a series DC voltage regulating method based on a dual-loop architecture. The series DC voltage regulating method based on a dual-loop architecture in this embodiment includes steps S1 to S3, which are described in detail as follows:

[0062] Step S1, set the switching state of the DC loop according to the load size at the end of the transmission line.

[0063] As Figure 2As shown in the figure, the traditional series-type DC voltage regulating device is connected in series to the power transmission line. The rectifier, i.e., the AC / DC module in the figure, is connected in series to the head end of the power transmission line, and the inverter, i.e., the DC / AC module in the figure, is connected in series to the tail end of the power transmission line. Affected by the series connection, the voltage regulating device needs to operate continuously for a long time to ensure that the power transmission line can continuously provide sufficient power to the end users. However, long-term operation will affect the service life of the voltage regulating equipment, resulting in high equipment costs. Moreover, when the voltage regulating device fails, power outages are required for maintenance, and the power transmission line can only resume operation after the fault is eliminated. Therefore, when the device fails, the impact range on the operation of the power transmission line is large, resulting in poor reliability of the power transmission system.

[0064] Figure 3 What is provided is the topology of the traditional parallel-type voltage regulating device. As shown in the figure, the AC / DC module is connected in parallel to the head end of the power transmission line, and the DC / AC module is connected in parallel to the tail end of the power transmission line. Because two new DC power transmission lines are added between the rectifier and the inverter, and the parallel connection enables maintenance without power outages when the rectifier and the inverter fail, which will not affect the operation of the power transmission line. However, the voltage regulating device will only start to rectify when it detects low voltage at the tail end. At other times, the voltage regulating device is in a shutdown or standby state. Therefore, in a parallel environment, the voltage regulating device cannot participate in high-voltage rectification, so the voltage regulating device cannot give full play to its advantages. At the same time, due to the parallel connection method at the tail end, the voltage regulating device has limited compensation ability for unbalanced voltage.

[0065] In view of the advantages and disadvantages of the above traditional voltage regulation methods, the embodiments of the present application propose an improved double-loop series-type DC voltage regulation topology. This structure includes two DC voltage regulating devices and two DC loops. They are the first DC voltage regulating device, the first DC loop, the second DC voltage regulating device, and the second DC loop respectively. The lines used for these two DC loops are the original four-wire AC lines.

[0066] As Figure 4 shown is the improved double-loop series-type voltage regulating device topology provided by the embodiments of the present application. In the figure, the first DC voltage regulating device includes a rectifier main machine 1 and an inverter slave machine 1, and the second DC voltage regulating device includes a rectifier main machine 2 and an inverter slave machine 2. There are two rectifier modules in both the rectifier main machine 1 and the rectifier main machine 2, and there are two inverter modules in both the inverter main machine 1 and the inverter main machine 2, which respectively complete the AC / DC rectification work and the DC / AC inversion work. Between the rectifier main machine 1 and the inverter main machine 1, they are connected by a ±375V DC power transmission line, that is, the first DC loop. Between the rectifier main machine 2 and the inverter main machine 2, they are also connected by a ±375V DC power transmission line, that is, the second DC loop. Among them, every two AC lines form a DC loop, realizing the improvement of the original four-wire AC line into the DC double-line loop provided by the embodiments of the present application, so as to significantly reduce the line cost.

[0067] The rectifier main units 1 and 2 are connected to the outgoing line side of the transformer at the head end of the transmission line, and the inverter main units 1 and 2 are connected to the load side at the end of the transmission line. These two sets of DC voltage regulating devices are in a parallel mode with each other. In Figure 4 there are also four bypass switches, namely Q1, Q2, Q3, and Q4. By controlling the switching states of the bypass switches at different positions, the input of different modules and different DC circuits in the DC voltage regulating device can be switched. Among them, these bypass switches are generally in the off state, and when both sets of DC voltage regulating devices fail, the corresponding bypass switches are closed to switch the circuit to AC power supply.

[0068] As Figure 5 shown is the improved dual-loop series-type DC voltage regulating topology structure provided by the embodiment of the present application. In the figure, both the rectifier main units 1 and 2 include two rectifier modules, and both the inverter slave units 1 and 2 include two inverter modules. A single power conversion module can also be switched on and off through the opening and closing of the bypass switch. By controlling the switching of the bypass switches at different positions, the input states and input quantities of different modules in the device can be controlled to ensure the power supply demand of the system.

[0069] Furthermore, Figure 6 shows the topology structure of the rectifier module or the inverter module. For the convenience of explanation, the rectifier module or the inverter module will be collectively referred to as the power conversion module hereinafter. As shown in the figure, the power conversion module adopts a T-type three-level three-phase four-leg topology structure, and there are 4 power switch devices on each leg, all made of silicon carbide material. Compared with silicon material, silicon carbide material has higher bandgap width, better high-temperature stability, a breakdown electric field strength one order of magnitude higher, and an electron mobility that can remain relatively stable under high-temperature and high-electric-field conditions. These properties enable the power switch devices made of silicon carbide to still maintain good stability and reliability in a high-frequency and high-voltage working environment, avoiding the occurrence of adverse situations such as excessive switching losses, thermal runaway, and avalanche breakdown, and further improving the overall performance of the voltage regulating device.

[0070] In addition, in the embodiments of the present application, the four interfaces of the ABCN four phases on the AC side of the rectification module are respectively connected to the ABCN four phases on the output side of the low-voltage distribution network transformer. The DC+ and DC- on the DC side of the rectification module and the DC+ and DC- on the DC side of the inversion module are connected through a DC bus. The four interfaces of the ABCN four phases on the AC side of the inversion module are respectively connected to the ABCN four phases of the end user. Compared with the traditional three-phase three-leg topology, the T-type three-level three-phase four-leg topology of the power conversion module provided in the embodiments of the present application adds a fourth leg, namely the N-phase leg, compared with the conventional topology. The midpoint output of this leg is filtered by an inductor on the leg side and then connected to the neutral point of the filtering capacitors of the A, B, and C phases, and output to the N phase of the power grid, and there is no grid-side filtering inductor for the N phase. The fourth leg provides an independent path for zero-sequence current. When the three-phase load is unbalanced, the zero-sequence potential is adjusted by controlling the fourth leg to avoid the mutual influence of zero-sequence current among the three phases, so that the voltage of each phase can be independently controlled, and the decoupling of the three-phase voltage is realized.

[0071] Therefore, the rectification module and the inversion module of the three-level three-phase four-leg based on all silicon carbide power switching devices can greatly improve the freedom and accuracy of phase voltage control, and are especially suitable for the single-phase unbalanced working conditions frequently occurring in low-voltage distribution networks. At the same time, the bidirectional PWM commutation technology is adopted to realize the output of arbitrary current in four quadrants, and the bidirectional voltage regulation function of the device can be realized.

[0072] Based on the above-mentioned topological structures of the DC voltage regulation device and the DC circuit, the embodiments of the present application can determine the number of DC circuits that should be put into operation for voltage regulation currently by obtaining the real-time load conditions, and can also control the input states of different DC circuits and the modules in the device by switching the bypass switches in the topological structures of the rectification module and the inversion module, so as to ensure the stable operation of the system.

[0073] Specifically, the end loads of the transmission line mainly include two situations: full-power operation condition or non-full-power operation condition.

[0074] The full-power operation condition means that the operating power of the end device reaches the rated maximum value under normal operation. At this time, the end device consumes a large amount of power and requires the transmission line to provide sufficient power to maintain stable operation. Therefore, the first DC circuit and the second DC circuit are both set to the connected state through the bypass switch to be put into operation.

[0075] Exemplarily, on the transformer side, two rectification modules of the rectification mainframe 1 and one rectification module of the rectification mainframe 2 are put into operation, or two rectification modules of the rectification mainframe 2 and one rectification module of the rectification mainframe 1 are put into operation; on the end load side, two inversion modules of the inversion slave 1 and one inversion module of the inversion slave 2 are put into operation, or two inversion modules of the inversion slave 2 and one inversion module of the inversion slave 1 are put into operation to ensure sufficient power supply to the end user.

[0076] Under the non-full power operation condition, since the amount of electrical energy required by end-users is small, only one DC circuit can meet the demand of the end load. Moreover, considering that too long an input time of the DC circuit will lead to a long continuous operation time of the DC voltage regulating device, which will shorten the service life of the equipment. Therefore, in the embodiment of the present application, the first DC circuit and the second DC circuit operate alternately. When it is detected that the input operation time of a certain DC circuit is too long, that is, it exceeds the preset first operation time, it is bypassed through a bypass switch, and the other DC circuit is connected to be put into operation. In this way, the input operation time of the first DC circuit and the second DC circuit can be made uniform to the greatest extent.

[0077] As an improvement of the above solution, under the non-full power operation condition, the embodiment of the present application also takes into account the size of the end load to adjust the number of rectification modules or power conversion modules put into operation in the DC voltage regulating device.

[0078] Exemplarily, when the end load is small, only a single module on one DC circuit needs to be put into operation. For example, when the first DC circuit is put into operation and the second DC circuit is bypassed, any one of the two modules in the rectification host 1 and the inversion slave 1 can be selected to be put into operation. For example, select Figure 3 the rectification module 1-1 and the inversion module 1-1 in it to participate in voltage regulation; when the end load is large, both modules on one DC circuit are put into operation, that is, it is necessary to put into operation Figure 3 the rectification module 1-1, the rectification module 1-2, the inversion module 1-1 and the inversion module 1-2 in it, or put into operation the rectification module 2-1, the rectification module 2-2, the inversion module 2-1 and the inversion module 2-2.

[0079] Through the above solution, stable operation of the distribution network can be achieved under different actual load conditions, normal power supply to the remote end can be guaranteed, not only the service life of the equipment is extended, but also the operation stability is greatly improved.

[0080] Step S2, set the switching state of the DC voltage regulating device according to the equipment fault situation on the DC circuit.

[0081] In the embodiment of the present application, it also detects whether there are faults in the DC voltage regulating device and the DC circuit to control the switching state.

[0082] First, determine the number of faulty locations. When there is a fault at one location of the voltage regulating equipment on only one DC circuit, it is only necessary to disconnect the module where the fault is located through the bypass switch, and the other modules can operate normally to support the operation under full-power operation conditions and non-full-power operation conditions. If two modules in a certain DC voltage regulating device are abnormal, that is, a single DC circuit is abnormal, then bypass the DC circuit corresponding to the faulty DC voltage regulating device, and put the other DC circuit into operation. In this case, it can still support the long-term operation of 80% of the load power. Moreover, the bypassed module can also replace the faulty circuit through live maintenance, ensuring that the voltage regulation operation can still be normally executed during the repair of the fault and guaranteeing normal power supply to the remote end.

[0083] If there is an extreme situation where the DC voltage regulating devices on both DC circuits fail, then close the bypass switch on the line to bypass all the DC voltage regulating devices, and switch the DC double circuit to a four-wire ABCN four-phase AC power transmission to supply power to the end users. Since both DC voltage regulating devices are bypassed, the faults of the devices will not affect the normal operation of the AC power transmission line, and the devices can be repaired without power interruption. After the device faults are eliminated, the AC power transmission line can be switched back to DC power transmission by disconnecting the bypass switch, and the first DC voltage regulating device and the second DC voltage regulating device can both be put into operation again to achieve the efficient and stable operation of the distribution network system.

[0084] Step S3: Based on the comparison result between the terminal voltage of the power transmission line and the preset normal voltage range, regulate the magnitude and direction of the current in the connected DC voltage regulating device and the DC circuit to regulate the terminal voltage.

[0085] In the embodiment of the present application, because the T-type three-level three-phase four-leg topology structure based on the bidirectional PWM commutation technology is adopted inside the DC voltage regulating device, which can not only achieve independent control of three-phase voltages but also realize four-quadrant arbitrary current output, so this topology scheme can control the input states of different DC circuits and modules in the device according to the actual load size at the terminal, and can also adjust the magnitude and direction of the current in the topology by changing the duty ratio of the PWM signal and the control signal sequence of the power switch devices, so as to realize low-voltage governance and high-voltage governance at the terminal. Among them, the PWM technology (Pulse-Width Modulation) is also called pulse width modulation technology, which is a technology for controlling a circuit and achieves the purpose of adjusting voltage and frequency by changing the ratio of the conduction time to the total time, that is, the duty ratio.

[0086] In the embodiment of the present application, the PWM technology adjusts the output current of the DC voltage regulating device by adjusting the PWM duty cycle of the power switching devices in the rectification module and the inversion module, so as to achieve the purpose of regulating the terminal voltage. Among them, the terminal voltage depends on the output of the inverter. Therefore, the inverter needs to work in the current source mode to ensure the stability of the voltage amplitude, frequency and phase of the terminal power grid.

[0087] The terminal voltage is monitored in real time by the signal acquisition system and compared with the preset normal voltage range. If the terminal voltage is less than the normal voltage range, the electrical energy received by the terminal user is insufficient, and the DC voltage regulating device needs to start the low voltage regulation mode; if the terminal voltage is greater than the normal voltage range, it is easy to cause damage to the terminal equipment, and the DC voltage regulating device needs to start the high voltage regulation mode.

[0088] In the low voltage regulation mode, the PWM duty cycle in the rectification module and the inversion module is increased by extending the conduction time of the power switching device, so that the effective value of the output current of the DC voltage regulating device increases. Specifically: measure the line resistance from the output end of the inverter of the DC voltage regulating device to the terminal equipment and the expected load current, calculate the voltage drop of the terminal voltage of the transmission line, increase the PWM duty cycle of the power switching device in the inversion module, so that the increased value of the output voltage amplitude can cover the line voltage drop value, and enable the terminal equipment to receive sufficient voltage.

[0089] In the high voltage regulation mode, not only the effective value of the output current of the DC voltage regulating device needs to be changed, but also the output direction of the circuit current needs to be adjusted. Specifically: when a high voltage appears at the terminal, by changing the control signal sequence of the power switching device in the rectification module or the inversion module, the current flow direction of the inversion module is changed from the original from the DC side to the AC side to from the AC side to the DC side. At this time, the output current of the DC voltage regulating device is out of phase with the voltage of the power grid. Then, according to the line voltage drop and the terminal voltage value, adjust the PWM duty cycle of the power switching device in the inversion module, and adjust the actual output current of the DC voltage regulating device to reduce the terminal voltage and return it to the normal voltage range.

[0090] Implementing the embodiment of the present application has the following beneficial effects:

[0091] In the embodiment of the present application, a series-type DC voltage regulating topology is arranged on the transmission line, which includes two DC voltage regulating devices and two DC circuits. Each DC circuit is connected in series with a DC voltage regulating device. The rectifier module of the DC voltage regulating device is connected to the outgoing line side of the transformer of the transmission line, and the inverter module is connected to the end load side of the transmission line to achieve the end voltage governance through the DC voltage regulating device. Determine how many DC circuits are needed to participate in the voltage governance according to the size of the end load, so as to reasonably plan the operation time of the DC circuits and meet the power demand as quickly as possible, and avoid affecting the service life of a circuit due to too long operation time. In addition, which device is used for voltage regulation is set according to the number of faults occurring in the DC voltage regulating device. The voltage regulating device with too many faults is bypassed and repaired without power interruption, and the voltage regulating device with no faults or very few faults is put into operation, so as to ensure the normal operation of the DC circuit even under fault conditions and maintain normal power supply at the far end. Finally, for the situation of too low or too high end voltage, by adjusting the control signal sequence and PWM duty ratio of the power switch device, the magnitude and direction of the current in the DC voltage regulating device and the DC circuit are adjusted to change the magnitude of the output current, thereby affecting the magnitude of the end voltage, so that the end voltage is maintained within a stable range, realizing the precise governance of the end voltage and maintaining the operation stability of the power system.

[0092] Second Embodiment

[0093] Furthermore, in order to implement the series-type DC voltage regulating device based on the dual-loop architecture corresponding to the above method embodiment to achieve the corresponding functions and technical effects, Figure 7 A structural diagram of a series-type DC voltage regulating device based on a dual-loop architecture is provided. For the convenience of description, only the parts related to this embodiment are shown. The series-type DC voltage regulating device based on the dual-loop architecture provided by the embodiment of the present application includes:

[0094] A loop setting module 201, configured to set the switching state of the DC loop according to the size of the end load of the transmission line; wherein, the DC loop includes a first DC loop and a second DC loop.

[0095] In the embodiment of the present application, the size of the end load is collected in real time to determine whether the current transmission line is in a preset full-power operation condition or a preset non-full-power operation condition. If it is the non-full-power operation condition, the first DC loop and the second DC loop are set to alternately enter the connected state. If it is the full-power operation condition, the first DC loop and the second DC loop are both set to the connected state.

[0096] A voltage regulation device setting module 202 is configured to set the switching state of a DC voltage regulation device according to the equipment fault conditions on the DC circuit. Among them, the DC voltage regulation device includes a first DC voltage regulation device and a second DC voltage regulation device. The first DC voltage regulation device is connected in series on a first DC circuit, and the second DC voltage regulation device is connected in series on a second DC circuit.

[0097] First, determine the number of fault locations. When only one location of the voltage regulation equipment on a single DC circuit fails, it is only necessary to disconnect the module where the fault occurs through a bypass switch, and other modules can operate normally to support the operation under full-power operation conditions and non-full-power operation conditions. If two modules in a certain DC voltage regulation device are abnormal, that is, a single DC circuit is abnormal, then bypass the DC circuit corresponding to the DC voltage regulation device with the fault and put the other DC circuit into operation. In this case, it can still support the long-term operation of 80% of the load power. Moreover, the bypassed module can also replace the faulty circuit through live maintenance, ensuring that the voltage regulation operation can still be normally executed during the repair of the fault and guaranteeing normal power supply to the remote end.

[0098] If it is an extreme case where the DC voltage regulation devices on both DC circuits fail, then close the bypass switches on the line to bypass all the DC voltage regulation devices, and switch the DC double circuit to a four-wire ABCN four-phase AC power transmission to supply power to the end users. Since both DC voltage regulation devices are bypassed, the faults of the devices will not affect the normal operation of the AC power transmission line, and the devices can be repaired without power interruption. After the device faults are eliminated, the AC power transmission line can be switched back to DC power transmission by disconnecting the bypass switches, and the first DC voltage regulation device and the second DC voltage regulation device can be put into operation again to achieve the efficient and stable operation of the distribution network system.

[0099] A voltage regulation module 203 is configured to regulate the magnitude and direction of the current in the DC voltage regulation device and the DC circuit in the connected state based on the comparison result between the terminal voltage of the power transmission line and the preset normal voltage range, so as to regulate the terminal voltage.

[0100] In the embodiment of the present application, since the DC voltage regulation device internally adopts a T-type three-level three-phase four-leg topology based on bidirectional PWM commutation technology, it can not only achieve independent control of three-phase voltages, but also achieve arbitrary current output in four quadrants. Therefore, this topology scheme can control the input states of different DC circuits and modules within the device according to the actual load size at the end, and can also adjust the magnitude and direction of the current within the topology by changing the duty cycle of the PWM signal and the control signal sequence of the power switch devices, so as to realize low-voltage governance and high-voltage governance at the end. Among them, the PWM technology (Pulse-Width Modulation) is also known as the pulse width modulation technology, which is a technology for controlling a circuit. By changing the ratio of the conduction time to the total time, that is, the duty cycle, the purpose of adjusting the voltage and frequency is achieved.

[0101] In the embodiment of the present application, the PWM technology adjusts the magnitude of the output current of the DC voltage regulation device by adjusting the PWM duty cycle of the power switch devices in the rectification module and the inversion module, so as to achieve the purpose of governing the terminal voltage. Among them, the terminal voltage depends on the output of the inverter, so the inverter needs to work in the current source mode to ensure the stability of the voltage amplitude, frequency and phase of the terminal power grid.

[0102] The terminal voltage is monitored in real time through the signal acquisition system and compared with the preset normal voltage range. If the terminal voltage is less than the normal voltage range, the electric energy received by the terminal user is insufficient, and the DC voltage regulation device needs to start the low-voltage governance mode; if the terminal voltage is greater than the normal voltage range, it is likely to cause damage to the terminal equipment, and the DC voltage regulation device needs to start the high-voltage governance mode.

[0103] In the low-voltage governance mode, the PWM duty cycle in the rectification module and the inversion module is increased by extending the conduction time of the power switch devices, so that the effective value of the output current of the DC voltage regulation device increases. Specifically: measure the line resistance from the output end of the inverter of the DC voltage regulation device to the terminal equipment and the expected load current, calculate the voltage drop of the terminal voltage of the transmission line, increase the PWM duty cycle of the power switch devices in the inversion module, so that the increased value of the output voltage amplitude can cover the line voltage drop value, and enable the terminal equipment to receive sufficient voltage.

[0104] In the high-voltage governance mode, not only the effective value of the output current of the DC voltage regulating device needs to be changed, but also the output direction of the current needs to be adjusted. Specifically, when a high voltage appears at the end, by changing the control signal sequence of the power switching devices in the rectifier module or the inverter module, the current flow direction of the inverter module is changed from the original from the DC side to the AC side to from the AC side to the DC side. At this time, the output current of the DC voltage regulating device and the voltage of the power grid are out of phase. Then, according to the line voltage drop and the end voltage value, the PWM duty cycle of the power switching devices in the inverter module is adjusted to adjust the actual output current of the DC voltage regulating device, so that the end voltage is reduced and restored to the normal voltage range.

[0105] In some embodiments, the loop setting module 201 further includes:

[0106] The traditional series-type DC voltage regulating device is connected in series on the transmission line. The rectifier is connected in series at the head end of the transmission line, and the inverter is connected in series at the end of the transmission line. Affected by the series connection, the voltage regulating device needs to run continuously for a long time to ensure that the transmission line can continuously provide sufficient power to the end users. However, long-term operation will affect the service life of the voltage regulating equipment, resulting in a high equipment cost. Moreover, when the voltage regulating device fails, power outages are required for maintenance. The transmission line can only resume operation after the fault is eliminated. Therefore, when the device fails, the impact range on the operation of the transmission line is large, resulting in poor reliability of the power transmission system.

[0107] The traditional parallel-type voltage regulating device has the rectifier connected in parallel at the head end of the transmission line and the inverter connected in parallel at the end of the transmission line. Because two new DC transmission lines are added between the rectifier and the inverter, and the parallel connection enables maintenance without power outages when the rectifier and the inverter fail, which does not affect the operation of the transmission line. However, the voltage regulating device will only start to govern when it detects a low voltage at the end. At other times, the voltage regulating device is in a shutdown or standby state. Therefore, in a parallel environment, the voltage regulating device cannot participate in high-voltage governance. As a result, the voltage regulating device cannot fully exert its advantages. At the same time, due to the parallel connection method at the end, the voltage regulating device has limited compensation ability for unbalanced voltages.

[0108] In view of the advantages and disadvantages of the above traditional voltage regulation methods, the embodiments of the present application propose an improved double-loop series-type DC voltage regulation topology structure. This structure includes two DC voltage regulating devices and two DC loops. They are the first DC voltage regulating device, the first DC loop, the second DC voltage regulating device, and the second DC loop respectively. The lines used for these two DC loops are the original AC four-wire system lines. Every two AC lines form a DC loop, realizing the improvement of the original four-wire AC line into the DC double-line loop provided by the embodiments of the present application, so as to significantly reduce the line cost.

[0109] Among them, the rectifier and the inverter of the first DC voltage regulating device are connected through the first DC circuit, and the rectifier and the inverter of the second DC voltage regulating device are connected through the second DC circuit. The first DC voltage regulating device and the second DC voltage regulating device are in a parallel mode with each other.

[0110] Optionally, in the embodiment of the present application, both the first DC circuit and the second DC circuit are ±375V DC transmission lines.

[0111] In addition, there are four bypass switches to control the switching states of different modules and different DC circuits in the DC voltage regulating device. These bypass switches are generally in the off state. When both sets of DC voltage regulating devices fail, the corresponding bypass switches are closed to switch the circuit to AC power supply.

[0112] Therefore, the improved dual-loop series DC voltage regulating topology provided by the embodiment of the present application, in which both rectifier hosts include two rectifier modules, both inverter slaves include two inverter modules, and a single power conversion module can also be switched on and off through the opening and closing of the bypass switch. By controlling the switching of the bypass switches at different positions, the input states and input quantities of different modules in the device are controlled to ensure the power supply demand of the system.

[0113] Further, for the convenience of explanation, the rectifier module or the inverter module will be collectively referred to as the power conversion module hereinafter. In the embodiment of the present application, the power conversion module adopts a T-type three-level three-phase four-leg topology structure. There are 4 power switching devices on each leg, all made of silicon carbide material. Compared with silicon material, silicon carbide material has higher bandgap width, better high-temperature stability, breakdown electric field strength one order of magnitude higher, and electron mobility that can remain relatively stable under high-temperature and high-electric-field conditions. These properties enable the power switching devices made of silicon carbide to maintain good stability and reliability in a high-frequency and high-voltage working environment, avoiding adverse situations such as excessive switching losses, thermal runaway, and avalanche breakdown, and further improving the overall performance of the voltage regulating device.

[0114] In addition, in the embodiments of the present application, the four interfaces of the ABCN four phases on the AC side of the rectification module are respectively connected to the ABCN four phases on the output side of the low-voltage distribution network transformer. The DC+ and DC- on the DC side of the rectification module and the DC+ and DC- on the DC side of the inversion module are connected through a DC bus. The four interfaces of the ABCN four phases on the AC side of the inversion module are respectively connected to the ABCN four phases of the end user. Compared with the traditional three-phase three-leg topology, the T-type three-level three-phase four-leg topology of the power conversion module provided in the embodiments of the present application adds a fourth leg, namely the N-phase leg, compared with the conventional topology. The midpoint output of this leg is filtered by a leg-side filter inductor and then connected to the neutral point of the filter capacitors of the A, B, and C phases, and output to the N phase of the power grid, and there is no grid-side filter inductor in the N phase. The fourth leg provides an independent path for zero-sequence current. When the three-phase load is unbalanced, the zero-sequence current is avoided from affecting each other among the three phases by controlling the fourth leg to adjust the neutral line potential, so that the voltages of each phase can be independently controlled, and the decoupling of the three-phase voltages is realized.

[0115] Therefore, the rectification module and the inversion module of the three-level three-phase four-leg based on all silicon carbide power switching devices can greatly improve the freedom and accuracy of single-phase voltage control, and are especially suitable for single-phase unbalanced working conditions frequently occurring in low-voltage distribution networks. At the same time, the bidirectional PWM commutation technology is adopted to realize the arbitrary current output in four quadrants, and the bidirectional voltage regulation function of the device can be realized.

[0116] Based on the above-mentioned topology structures of the DC voltage regulating device and the DC circuit, the embodiments of the present application can determine the number of DC circuits that should be put into operation for voltage regulation according to the obtained real-time load conditions, and can also control the input states of different DC circuits and the modules in the device by switching the bypass switches in the topology structures of the rectification module and the inversion module, so as to ensure the stable operation of the system.

[0117] Specifically, the end loads of the transmission line mainly include two situations: full-power operation condition or non-full-power operation condition.

[0118] The full-power operation condition means that the operating power of the end equipment reaches the rated maximum value under normal operation. At this time, the end equipment consumes a large amount of power and requires the transmission line to provide sufficient power to maintain stable operation. Therefore, the first DC circuit and the second DC circuit are both set to the connected state through the bypass switch to be put into operation.

[0119] Under the non-full-power operation condition, since the amount of electrical energy required by the end users is small, only one DC loop can meet the demand of the end load. Moreover, considering that too long an input time of the DC loop will lead to a long continuous operation time of the DC voltage regulating device and shorten the equipment life, the embodiments of the present application adopt an alternating operation mode of the first DC loop and the second DC loop. When it is detected that the input operation time of a certain DC loop is too long, that is, exceeding the preset first operation time, it is bypassed through a bypass switch, and the other DC loop is connected and put into operation, so that the input operation time of the first DC loop and the second DC loop can be maximally balanced.

[0120] As an improvement of the above solution, under the non-full-power operation condition, the embodiments of the present application also consider the size of the end load to adjust the number of rectifier modules or power conversion modules put into operation in the DC voltage regulating device.

[0121] Exemplarily, when the end load is small, only a single module on one DC loop needs to be put into operation; when the end load is large, both modules on one DC loop are put into operation.

[0122] Through the above solution, stable operation of the distribution network can be realized under different actual load conditions, normal power supply to the remote end can be guaranteed, not only the equipment life is prolonged, but also the operation stability is greatly improved.

[0123] Implementing the embodiments of the present application has the following beneficial effects:

[0124] The embodiments of the present application set a series DC voltage regulating topology structure on the transmission line, which includes two DC voltage regulating devices and two DC loops. Each DC loop is connected in series with a DC voltage regulating device. The rectifier module of the DC voltage regulating device is connected to the transformer outlet side of the transmission line, and the inverter module is connected to the end load side of the transmission line to realize end voltage governance through the DC voltage regulating device. Determine how many DC loops are required to participate in voltage governance according to the size of the end load, reasonably plan the operation time of the DC loops while meeting the power demand as quickly as possible, and avoid affecting the service life due to too long an input operation time of one loop. In addition, which device is used for voltage regulation is set according to the number of faults occurring in the DC voltage regulating device. The voltage regulating device with too many faults is bypassed and repaired without power interruption, and the voltage regulating device without faults or with very few faults is put into operation, so that normal operation of the DC loop can be guaranteed even in case of faults, and normal power supply to the remote end can be maintained. Finally, for the situation of too low or too high end voltage, by adjusting the control signal sequence and PWM duty ratio of the power switch device, the magnitude and direction of the current in the DC voltage regulating device and the DC loop are adjusted to change the magnitude of the output current, thereby affecting the magnitude of the end voltage, so that the end voltage is maintained within a stable range, realizing precise governance of the end voltage and maintaining the operation stability of the power system.

[0125] Third Embodiment

[0126] Furthermore Figure 8 It is a structural diagram of a series DC voltage regulation system based on a dual-loop architecture provided by an embodiment of the present application. The series DC voltage regulation system based on a dual-loop architecture provided by the embodiment of the present application includes a series DC voltage regulation device and a series DC voltage regulation topology.

[0127] The series DC voltage regulation topology is connected in series on the transmission line and includes a first DC voltage regulation device, a first DC loop, a second DC voltage regulation device, and a second DC loop. When a fault occurs in the DC voltage regulation device, the DC dual-loop can be changed to the original four-wire AC line through the bypass switch in the series DC voltage regulation topology.

[0128] The first DC voltage regulation device includes a first rectifier main unit and a first inverter slave unit; the second DC voltage regulation device includes a second rectifier main unit and a second inverter slave unit. The internal compositions and functions of the first DC voltage regulation device and the second DC voltage regulation device are the same.

[0129] In the embodiment of the present application, both the first rectifier main unit and the second rectifier main unit include two rectifier modules, and both the first inverter slave unit and the second inverter slave unit include two inverter modules.

[0130] The rectifier module and the inverter module in the first DC voltage regulation device are connected through the first DC loop, and the rectifier module and the inverter module in the second DC voltage regulation device are connected through the second DC loop. The first DC voltage regulation device and the second DC voltage regulation device are in a parallel mode with each other.

[0131] The rectifier module is connected to the outlet side of the transformer of the transmission line, and the inverter module is connected to the end load side of the transmission line.

[0132] The input and disconnection of the rectifier module and the inverter module can be controlled through the bypass switches of the first DC voltage regulation device and the second DC voltage regulation device. Among them, the bypass switch is default to the off state under normal circumstances.

[0133] Both the rectifier module and the inverter module are based on the T-type three-level three-phase four-leg topology. Each leg on the T-type three-level three-phase four-leg topology has four power switching devices, all made of silicon carbide material, which can have higher bandgap width, better high-temperature stability, a breakdown electric field strength one order of magnitude higher, and an electron mobility that can remain relatively stable under high-temperature and high-electric-field conditions. These performances enable the power switching devices made of silicon carbide to still maintain good stability and reliability in a high-frequency and high-voltage working environment, avoiding the occurrence of adverse conditions such as excessive switching loss, thermal runaway, and avalanche breakdown, and further improving the overall performance of the voltage regulation device.

[0134] The four interfaces of the four phases ABCN on the AC side of the rectifier module are respectively connected to the four phases ABCN on the output side of the low-voltage distribution network transformer. The DC+ and DC- on the DC side of the rectifier module and the DC+ and DC- on the DC side of the inverter module are connected through a DC bus. The four interfaces of the four phases ABCN on the AC side of the inverter module are respectively connected to the four phases ABCN of the end user. Therefore, compared with the conventional topology, the T-type three-level three-phase four-leg topology of the power conversion module provided in the embodiment of the present application adds a fourth leg, that is, the N-phase leg. The midpoint output of this leg is filtered by the leg-side filter inductor and then connected to the neutral point of the three-phase filter capacitors of A, B, and C, and output to the N phase of the power grid, and there is no grid-side filter inductor in the N phase. The fourth leg provides an independent path for the zero-sequence current. When the three-phase load is unbalanced, the zero-sequence current is adjusted by controlling the fourth leg to avoid the mutual influence of the zero-sequence current among the three phases, so that the voltages of each phase can be independently controlled, and the decoupling of the three-phase voltages is realized.

[0135] Therefore, the rectifier module and the inverter module of the three-level three-phase four-leg based on all silicon carbide power switching devices can greatly improve the freedom and accuracy of the phase voltage control, and are especially suitable for the single-phase unbalanced working conditions frequently occurring in the low-voltage distribution network. At the same time, the bidirectional PWM commutation technology is adopted to realize the arbitrary current output in four quadrants, and the bidirectional voltage regulation function of the device can be realized.

[0136] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present application. It should be understood that the above are only specific embodiments of the present application and are not used to limit the protection scope of the present application. In particular, it is pointed out that for those skilled in the art, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A series DC voltage regulation method based on a dual-loop architecture, characterized in that, Including: Set the switching state of the DC circuit according to the magnitude of the terminal load of the transmission line; wherein, the DC circuit includes a first DC circuit and a second DC circuit, and the DC circuit is a transmission line connecting internal modules of the DC voltage regulating device; Set the switching state of the DC voltage regulating device according to the equipment fault condition on the DC circuit; wherein, the DC voltage regulating device includes a first DC voltage regulating device and a second DC voltage regulating device; the first DC voltage regulating device is connected in series on the first DC circuit, and the second DC voltage regulating device is connected in series on the second DC circuit; Based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, regulate the magnitude and direction of the current in the DC voltage regulating device and the DC circuit in the connected state to regulate the terminal voltage.

2. The series DC voltage regulation method based on a dual-loop architecture according to claim 1, characterized in that, The setting of the switching state of the DC circuit according to the magnitude of the terminal load of the transmission line is specifically: Collect the magnitude of the terminal load in real time to determine whether the current transmission line is in a preset full-power operation condition or a preset non-full-power operation condition; If it is the non-full-power operation condition, set the first DC circuit and the second DC circuit to alternately enter the connected state; If it is the full-power operation condition, set both the first DC circuit and the second DC circuit to the connected state.

3. The series DC voltage regulation method based on a dual-loop architecture according to claim 2, wherein, The setting of the first DC circuit and the second DC circuit to alternately enter the connected state is specifically: When one of the first DC circuit and the second DC circuit is set to the connected state, set the other circuit to the disconnected state; When the total duration of being set to the connected state exceeds the first operation time, switch the DC circuit in the connected state to the disconnected state.

4. The series DC voltage regulation method based on a dual-loop architecture according to claim 2, wherein Also including: Determine the number of rectifier modules and inverter modules participating in voltage regulation in the DC voltage regulating device according to the comparison result between the magnitude of the terminal load and a preset first threshold; wherein, the rectifier modules and inverter modules are based on a T-type three-level three-phase four-arm topology; Among them, the greater the magnitude of the terminal load is greater than the first threshold, the more rectifier modules and inverter modules participating in voltage regulation in the DC voltage regulating device.

5. The series DC voltage regulation method based on a dual-loop architecture according to claim 1, characterized in that, The setting of the switching state of the DC voltage regulating device according to the equipment fault condition on the DC circuit is specifically: Detect the equipment fault condition on the DC circuit and record the number of fault locations in the DC voltage regulating device; If there is only one fault location on any one of the DC voltage regulating devices, bypass the fault location and the DC voltage regulating device continues to operate; If there are multiple fault locations in any one of the DC voltage regulating devices, bypass the DC circuit corresponding to the DC voltage regulating device with the fault and put the other DC circuit into operation; If there are multiple fault locations in all the DC voltage regulating devices, bypass all the DC voltage regulating devices and switch the DC circuit to AC power transmission.

6. The series DC voltage regulation method based on a dual-loop architecture according to claim 5, wherein Also including: After completing the bypass operation, perform live maintenance on the DC voltage regulating device with the fault location, and then put the DC voltage regulating device after the maintenance back into operation by operating the bypass switch.

7. The series DC voltage regulation method based on a dual-loop architecture according to any one of claims 1 to 6, characterized in that, Based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, regulate the magnitude and direction of the current in the DC voltage regulating device and the DC loop in the connected state. Specifically: Collect the terminal voltage in real time and compare the terminal voltage with the normal voltage range. When the terminal voltage is greater than the normal voltage range, set the DC voltage regulating device in the connected state to the high voltage governance mode. When the terminal voltage is less than the normal voltage range, set the DC voltage regulating device in the connected state to the low voltage governance mode.

8. The series DC voltage regulation method based on a dual-loop architecture according to claim 7, characterized in that, The high voltage governance mode and the low voltage governance mode are specifically: In the high voltage governance mode, change the current direction of the inverter module in the DC voltage regulating device from the AC side to the DC side by adjusting the control signal sequence of the power switch device, and then adjust the output current magnitude of the DC voltage regulating device by adjusting the PWM duty cycle of the switch device in the inverter module to reduce the terminal voltage. In the low voltage governance mode, increase the PWM duty cycle of the switch device in the inverter module in the DC voltage regulating device to adjust the output current magnitude of the DC voltage regulating device to increase the terminal voltage.

9. A series DC voltage regulation device based on a dual-loop architecture, characterized in that, Including: A loop setting module, a voltage regulating device setting module, and a voltage regulating module; Among them, the loop setting module is used to set the switching state of the DC loop according to the magnitude of the terminal load of the transmission line. Among them, the DC loop includes a first DC loop and a second DC loop, and the DC loop is a transmission line connecting the internal modules of the DC voltage regulating device. The voltage regulating device setting module is used to set the switching state of the DC voltage regulating device according to the equipment failure situation on the DC loop. Among them, the DC voltage regulating device includes a first DC voltage regulating device and a second DC voltage regulating device; the first DC voltage regulating device is connected in series on the first DC loop, and the second DC voltage regulating device is connected in series on the second DC loop. The voltage regulating module is used to regulate the magnitude and direction of the current in the DC voltage regulating device and the DC loop in the connected state based on the comparison result between the terminal voltage of the transmission line and the preset normal voltage range, so as to regulate the terminal voltage.

10. A series DC voltage regulation system based on a dual-loop architecture, characterized in that, Including: A series DC voltage regulating device and a series DC voltage regulating topology; Among them, the series DC voltage regulating topology includes a first DC voltage regulating device, a first DC loop, a second DC voltage regulating device, and a second DC loop; The first DC voltage regulating device includes a first rectifier main unit and a first inverter slave unit; the second DC voltage regulating device includes a second rectifier main unit and a second inverter slave unit. Among them, the first rectifier main unit and the second rectifier main unit both include a plurality of rectifier modules, and the first inverter slave unit and the second inverter slave unit both include a plurality of inverter modules; The first rectifier main unit and the second rectifier main unit are respectively connected to the transformer outlet side of the transmission line; The first inverter slave unit and the second inverter slave unit are respectively connected to the terminal load side of the transmission line; The series DC voltage regulating device is used to execute the series DC voltage regulating method based on the dual-loop architecture according to any one of claims 1 to 7.

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