A direct current energy consumption device and control method

Abstract

The application belongs to the technical field of high-voltage direct current transmission, and particularly relates to a direct current energy consumption device and a control method. The device is composed of a series connection of a centralized energy consumption resistor and at least one energy consumption valve composed of a series connection of a plurality of voltage-dividing modules. After all the voltage-dividing modules are cut off, the surplus power is discharged through the centralized energy consumption resistor. The switching process of the voltage-dividing modules uses a ramping switching strategy, which reduces the voltage change rate on the resistor and the impact on the direct current system. The device has the characteristics of high performance, high reliability and low cost.

Description

Technical Field

[0001] This invention belongs to the field of high voltage direct current transmission technology, specifically relating to a DC energy consumption device and control method. Background Technology

[0002] Flexible DC transmission technology boasts advantages such as the absence of commutation failure, low voltage harmonic content, high waveform quality, and rapid adjustment of active and reactive power. These advantages have led to widespread application demands for flexible DC technology in power systems, such as the integration, collection, and transmission of large-scale clean energy and the supply of power to isolated passive loads. However, when flexible DC is applied to the transmission of new energy systems, if a fault occurs at the receiving end causing a voltage drop in the AC grid, active power cannot be transmitted or can only be partially transmitted to the AC grid. This excess active power causes a voltage rise in the DC transmission line, jeopardizing the safety of equipment such as flexible DC converter valves.

[0003] The existing technologies employ the following methods:

[0004] 1) such as Figure 1 As shown in the literature "DolWin1–Challenges of Connecting Offshore Wind Farms", power semiconductor devices are directly connected in series. When the DC voltage is too high, a resistor is switched on through the control of power electronic devices. The switching on of the resistor will cause the DC voltage to drop. When the rate of energy dissipation of the resistor exceeds the rate of energy accumulation on the DC side, the DC voltage will drop, the resistor discharge circuit will be turned off, and the DC voltage will rise again. The DC voltage is controlled by repeatedly switching the resistor branch on and off. The main problems with this method are: during the turn-off, it is difficult to ensure consistency due to the technical difficulty of turning off multiple power semiconductor switching devices at the same time. Once the turn-off is not synchronized, devices that turn on slowly or turn off quickly will be damaged by overvoltage. On the other hand, the power impact on the DC system is also relatively large when the energy dissipation resistor is switched on and off.

[0005] 2) The literature "A Novel DC Chopper With MOV-Based Modular Solid-State Switch and Concentrated Dissipation Resistor for ±400kV / 1100MW Offshore Wind VSC-HVDC System" and the patent "A DC Energy Dissipation Device" (application number: 202020347908.0) add parallel filter capacitors to the above centralized scheme. By adjusting the duty cycle of the device, the matching of discharged power and surplus power is achieved, and the DC voltage fluctuation is smooth and small during the discharge process. However, the difficulty of simultaneous switching of large-scale power electronic devices still exists, and the DC filter capacitor increases the cost of the device.

[0006] 3) such as Figure 2 As shown, the Chinese invention patent "An energy-consuming device and control method" (publication number: CN109245506B) distributes the energy-consuming resistors in multiple sub-modules. By adjusting the number of energy-consuming resistors, the discharge power is adjusted to achieve a balance between the discharge power and the surplus power, thereby reducing the fluctuation of DC voltage during energy consumption. However, this method is relatively expensive.

[0007] 4) such as Figure 3 and Figure 4 As shown, the Chinese invention patent "A DC Energy Consumption Device" (Publication No.: CN212392662U) adopts a centralized energy consumption device composed of half-bridge sub-modules connected in series. This can overcome the technical difficulty of directly switching large-scale power electronic devices and reduce the power impact on the DC system through ramp-up and shutdown. However, the sub-modules in this scheme absorb energy during ramp-up and shutdown, and this energy needs to be released into the DC system through the upper tube of the sub-module. The configuration of two power devices in one sub-module also increases the cost of the device. Summary of the Invention

[0008] The purpose of this invention is to provide a DC energy-consuming device and control method to solve the technical difficulties of simultaneously switching on and off multiple series power semiconductor switching devices and the problem of electrical impact on the system when the energy-consuming device is put into operation or deactivated.

[0009] To solve the above-mentioned technical problems, the present invention provides a control method for a DC energy-consuming device. The DC energy-consuming device is used to install on a DC line and includes an energy-consuming branch. A centralized energy-consuming resistor and an energy-consuming valve are connected in series on the energy-consuming branch. The energy-consuming valve includes multiple voltage divider sub-modules connected in series. The control method includes the following steps:

[0010] 1) When a fault occurs in the DC system, if the DC line voltage is greater than or equal to the trigger voltage, the voltage divider submodules will be disconnected one by one at a predetermined rate so that power can be discharged through the centralized energy dissipation resistor.

[0011] 2) Then, when the DC line voltage is less than or equal to the exit voltage, the sub-modules are engaged one by one at a predetermined rate;

[0012] 3) Then, when the DC voltage of the system is greater than or equal to the voltage setting threshold, the voltage divider sub-modules are cut off one by one at a predetermined rate so that the power is discharged through the centralized energy-consuming resistor and the DC line voltage is controlled within the required range.

[0013] Among them, the exit action voltage is less than the voltage setting threshold, and the voltage setting threshold is less than the trigger action voltage.

[0014] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0015] Furthermore, if the DC system is in normal operating condition, the voltage divider submodules are activated one by one at a predetermined rate.

[0016] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0017] Furthermore, during the normal operation of the DC line, it is necessary to perform voltage equalization operations on each voltage divider submodule in the energy consumption valve, and during the voltage equalization operation, a fixed number of voltage divider submodules with higher voltages are selected for disconnection.

[0018] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0019] Furthermore, the voltage divider module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series on the power consumption branch. The capacitor discharge resistor and the first diode are connected in parallel and then in series with the power transistor, and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in anti-parallel across the two ends of the power transistor, and a voltage equalization resistor is connected in parallel across the two ends of the capacitor.

[0020] Its beneficial effects are as follows: Compared with the centralized energy consumption device based on half-bridge submodule, the present invention reduces one power switching device in the submodule, thereby reducing the cost.

[0021] Furthermore, after the fault is recovered, all voltage divider submodules are locked out.

[0022] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0023] To address the aforementioned technical problems, the present invention also provides a DC energy dissipation device. This device is installed on a DC line and includes an energy dissipation branch. A centralized energy dissipation resistor and an energy dissipation valve are connected in series on the energy dissipation branch. The energy dissipation valve includes multiple voltage divider sub-modules connected in series. The DC energy dissipation device is controlled using the following method:

[0024] 1) When a fault occurs in the DC system, if the DC line voltage is greater than or equal to the trigger voltage, the voltage divider submodules will be disconnected one by one at a predetermined rate so that power can be discharged through the centralized energy dissipation resistor.

[0025] 2) Then, when the DC line voltage is less than or equal to the exit voltage, the sub-modules are engaged one by one at a predetermined rate;

[0026] 3) Then, when the DC voltage of the system is greater than or equal to the voltage setting threshold, the voltage divider sub-modules are cut off one by one at a predetermined rate so that the power is discharged through the energy-consuming resistor and the DC line voltage is controlled within the required range.

[0027] Among them, the exit action voltage is less than the voltage setting threshold, and the voltage setting threshold is less than the trigger action voltage.

[0028] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through centralized energy-consuming resistors. The switching process of the voltage divider modules uses a ramp-up and shutdown strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves system performance, solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices, and reduces the cost by eliminating one power switching device in the sub-module compared with centralized energy-consuming devices based on half-bridge sub-modules.

[0029] Furthermore, the voltage divider module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series on the power consumption branch. The capacitor discharge resistor and the first diode are connected in parallel and then in series with the power transistor, and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in anti-parallel across the two ends of the power transistor, and a voltage equalization resistor is connected in parallel across the two ends of the capacitor.

[0030] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0031] Furthermore, if the system is operating normally: if the DC system is in normal operating condition, the voltage divider sub-modules will be put into operation one by one at a predetermined rate.

[0032] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0033] Furthermore, during the normal operation of the DC line, it is necessary to perform voltage equalization operations on each voltage divider submodule in the energy consumption valve, and during the voltage equalization operation, a fixed number of voltage divider submodules with higher voltages are selected for disconnection.

[0034] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices.

[0035] Furthermore, after the fault is recovered, all voltage divider submodules are locked out.

[0036] Its beneficial effects are as follows: After cutting off all voltage divider modules, the present invention discharges surplus power through a centralized energy-consuming resistor. The switching process of the voltage divider modules uses a ramp-down switching strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system, improves the system performance, and solves the technical difficulty of simultaneously switching on multiple series power semiconductor switching devices. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a centralized DC power consumption device with power devices directly connected in series in the existing technology.

[0038] Figure 2 This is a schematic diagram of a centralized DC power dissipation device with distributed power dissipation resistors, which is a current technology.

[0039] Figure 3 It is an existing distributed DC energy consumption device;

[0040] Figure 4 It is a centralized DC power consumption device based on the existing technology of half-bridge sub-module;

[0041] Figure 5 This is a structural diagram of the DC energy-consuming device of the present invention;

[0042] Figure 6 This is a schematic diagram of the DC voltage control logic of the DC energy-consuming device of the present invention;

[0043] Figure 7 This is a schematic diagram of the ramp deployment and deployment of the sub-module of the present invention;

[0044] Figure 8-1 This is a simulation diagram of DC voltage in the actual application of the present invention;

[0045] Figure 8-2 This is a simulation diagram of the energy consumption switching effect in the actual application of the present invention;

[0046] Figure 8-3 This is a simulation diagram of the maximum submodule voltage in a practical application of the present invention;

[0047] Figure 8-4 The simulation diagram of the DC current effect of the energy-consuming device in the actual application of the present invention is shown. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0049] Example of a control method for DC power consumption devices:

[0050] The DC energy-consuming device of the present invention includes an energy-consuming circuit disposed on a DC line, such as... Figure 5 As shown, the DC energy dissipation device is used to install on a DC line and includes an energy dissipation branch. A centralized energy dissipation resistor and an energy dissipation valve are connected in series on the energy dissipation branch. The energy dissipation valve includes multiple voltage divider sub-modules connected in series. The voltage divider sub-module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series on the energy dissipation branch. The capacitor discharge resistor and the first diode are connected in parallel and then in series with the power transistor, and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in antiparallel across the two ends of the power transistor, and a voltage equalization resistor is connected in parallel across the two ends of the capacitor.

[0051] The DC energy-consuming device controls its operating status through DC voltage or activation / deactivation commands from the upper-level control and protection system. The specific control method is as follows:

[0052] 1) During normal system operation, the energy-consuming device is in standby mode, the semiconductor power switches of the voltage divider submodule in the energy-consuming valve are in the off state, the energy-consuming valve bears the entire DC voltage, and the voltage across the centralized energy-consuming resistor is approximately zero. During this period, in order to maintain the stability of the submodule voltage, the device needs to perform a voltage equalization operation on the submodules. This operation is performed once every control cycle or several control cycles: all submodule voltages are sorted, a fixed number of submodules with higher voltages are selected, their semiconductor power switches are turned on, and the capacitors of these submodules are discharged through the capacitor discharge resistor;

[0053] 2) When a system fault occurs, the surplus power causes the system DC voltage to rise, such as... Figure 6 As shown, it exceeds the set value U set1The power dissipation device will then be triggered to discharge power. To prevent accidental triggering of the power dissipation device during normal system operation, the trigger voltage U... set1 It should be higher than the normal fluctuation range of DC voltage. Taking into account the overvoltage withstand capability of the submarine cable, it is recommended to set the trigger voltage U. set1 It is between 1.1 pu and 1.2 pu of the rated DC voltage.

[0054] After the power dissipation device is triggered, the semiconductor power switches of all submodules will be turned on, and the entire DC voltage will be applied across the centralized power dissipation resistor to discharge excess power. Subsequently, the DC voltage will decrease as power is discharged, and when the DC voltage falls below the deactivation voltage U... set3 The device will then temporarily stop power discharge, disconnect the semiconductor power switch in the submodule, and allow the voltage to rise above the set voltage threshold U. set2 Then, the centralized power-consuming resistor is reinserted to control the DC voltage within a certain range, such as... Figure 6 As shown. Recommended voltage setting threshold U set2 Set the voltage to 1.05 pu to 1.07 pu of the rated DC voltage, and then exit the operating voltage U. set3 Set to 1.01 pu to 1.03 pu of the rated DC voltage.

[0055] 3) To reduce the power impact on the DC system and minimize DC voltage fluctuations during the switching of centralized power-consuming resistors, all sub-modules employ a ramp control strategy during the device switching process, such as... Figure 7 As shown, the device sequentially turns the power switches of the submodules on and off at a predetermined rate. The overall ramp time is recommended to be set to 2–4 ms, depending on the system conditions, meaning that the operation of all submodule power switches is gradually completed within 2–4 ms. During the submodule ramp-on / off process, the current charges the capacitors of the submodules whose power switches are still off. After the power switches are turned on, the capacitors discharge through the capacitor discharge resistor, thereby controlling the submodule voltage within the normal operating range. Figures 8-1 to 8-4 As shown.

[0056] The following example illustrates a DC power dissipation device connected to a 1000kV DC line. The centralized power dissipation resistor is 500 ohms, and the rated discharge power is 2000MW. The power dissipation valve comprises 500 voltage divider submodules. During normal system operation, there is no surplus power, and the power dissipation device is in standby mode. The power dissipation valve bears the DC voltage, with 499 voltage divider submodules in a locked state and one submodule with a higher voltage dynamically disconnected to maintain voltage balance. After a system fault, surplus power occurs. When the DC voltage exceeds the set operating voltage U... set1(Taking a rated voltage of 1.1pu as an example, which is 1100kV) After that, the power dissipation device is enabled, and according to the set 3ms ramp time, all voltage divider submodules are gradually disconnected, and the centralized power dissipation resistor gradually begins to discharge power; when the DC voltage is less than the set value U set3 (Taking a rated voltage of 1.02 pu as an example, which is 1020 kV) After that, the device disconnects the power switch of the submodule according to the set slope, and a voltage divider module with a higher voltage is dynamically disconnected to maintain voltage equalization; when the DC voltage is greater than the set value U again set2 (Taking a rated voltage of 1.06 pu as an example, which is 1060 kV) After that, the device cuts off all voltage divider submodules again according to the slope, and the centralized energy dissipation resistor begins to discharge power; this process repeats. During the entire power discharge process, the submodule capacitors are charged when the slope is turned on and off, and then discharged by the capacitor discharge resistor, and the submodule voltage fluctuates between 1000V and 2200V. Until a fault recovery command is received from the control protection, or the energy dissipation time reaches the resistor's allowable set value of 1.5s, the device will lock all voltage divider submodules (still cutting off one to maintain voltage equalization operation), wait for the resistor to cool down, and then re-enter standby mode.

[0057] This invention discharges excess power through a centralized energy-consuming resistor after disconnecting all voltage divider modules. The switching process of the voltage divider modules uses a ramp-up and shutdown strategy, which reduces the voltage change rate on the resistor and the impulse impact on the DC system. It features high performance, high reliability and low cost.

[0058] Example of a DC power consumption device:

[0059] The DC energy-consuming device of the present invention includes an energy-consuming circuit disposed on a DC line, such as... Figure 6 As shown, the DC energy dissipation device is used to install on a DC line and includes an energy dissipation branch. A centralized energy dissipation resistor and an energy dissipation valve are connected in series on the energy dissipation branch. The energy dissipation valve includes multiple voltage divider sub-modules connected in series. The voltage divider sub-module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series on the energy dissipation branch. The capacitor discharge resistor and the first diode are connected in parallel and then in series with the power transistor, and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in antiparallel across the two ends of the power transistor, and a voltage equalization resistor is connected in parallel across the two ends of the capacitor.

[0060] The DC energy consumption device control method used in the DC energy consumption device of the present invention has been described in detail in the embodiments of the DC energy consumption device control method, and will not be repeated here.

[0061] Specific implementation methods have been given above, but the present invention is not limited to the described implementation methods. The basic idea of ​​the present invention lies in the above basic scheme. For those skilled in the art, designing various modified models, formulas, and parameters based on the teachings of the present invention does not require creative effort. Changes, modifications, substitutions, and variations made to the implementation methods without departing from the principles and spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A control method for a DC energy-consuming device, characterized in that, A DC energy dissipation device is installed on a DC line and includes an energy dissipation branch. A centralized energy dissipation resistor and an energy dissipation valve are connected in series on the energy dissipation branch. The energy dissipation valve includes multiple voltage divider sub-modules connected in series. Each voltage divider sub-module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series with the first diode in parallel, and then connected in series with the power transistor and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in anti-parallel across the power transistor, and a voltage equalization resistor is connected in parallel across the capacitor. The control method includes the following steps: 1) When a fault occurs in the DC system, if the DC line voltage is greater than or equal to the trigger voltage, the voltage divider submodules will be disconnected one by one at a predetermined rate to discharge power through the centralized energy-consuming resistor. 2) Then, when the DC line voltage is less than or equal to the exit voltage, the sub-modules are engaged one by one at a predetermined rate; 3) Then, when the system DC voltage is greater than or equal to the voltage setting threshold, the voltage divider sub-modules are cut off one by one at a predetermined rate so that power can be discharged through the centralized energy-consuming resistor and the DC line voltage can be controlled within the required range. Among them, the exit action voltage is less than the voltage setting threshold, and the voltage setting threshold is less than the trigger action voltage.

2. The control method for a DC energy-consuming device according to claim 1, characterized in that, If the DC system is in normal operating condition, the voltage divider submodules will be put into operation one by one at a predetermined rate.

3. The control method for a DC energy-consuming device according to claim 2, characterized in that, During normal operation of the DC line, it is necessary to perform voltage equalization on each voltage divider module in the energy consumption valve. During the voltage equalization operation, a fixed number of voltage divider modules with higher voltage are selected for disconnection.

4. The control method for a DC energy-consuming device according to claim 1, characterized in that, The removal refers to turning on the power transistor of the submodule that needs to be removed and discharging the capacitor of the submodule through the capacitor discharge resistor.

5. The control method for a DC energy-consuming device according to claim 1, characterized in that, After the fault is recovered, all voltage divider submodules are locked.

6. A DC power dissipation device, characterized in that, A DC energy dissipation device is installed on a DC line and includes an energy dissipation branch. A centralized energy dissipation resistor and an energy dissipation valve are connected in series on the energy dissipation branch. The energy dissipation valve includes multiple voltage divider sub-modules connected in series. Each voltage divider sub-module includes a power transistor, a first diode, and a capacitor discharge resistor. The power transistor is connected in series with the first diode in parallel, and then connected in series with the power transistor and then in parallel with the capacitor. The cathode of the first diode is connected to the positive terminal of the capacitor. A second diode is connected in anti-parallel across the power transistor, and a voltage equalization resistor is connected in parallel across the capacitor. The DC energy dissipation device is controlled using the following method: 1) When a fault occurs in the DC system, if the DC line voltage is greater than or equal to the trigger voltage, the voltage divider submodules will be disconnected one by one at a predetermined rate to discharge power through the centralized energy-consuming resistor. 2) Then, when the DC line voltage is less than or equal to the exit voltage, the sub-modules are engaged one by one at a predetermined rate; 3) Then, when the DC voltage of the system is greater than or equal to the voltage setting threshold, the voltage divider sub-modules are cut off one by one at a predetermined rate so that the power is discharged through the energy-consuming resistor and the DC line voltage is controlled within the required range. Among them, the exit action voltage is less than the voltage setting threshold, and the voltage setting threshold is less than the trigger action voltage.

7. The DC power dissipation device according to claim 6, characterized in that, The removal refers to turning on the power transistor of the submodule that needs to be removed and discharging the capacitor of the submodule through the capacitor discharge resistor.

8. The DC power dissipation device according to claim 6, characterized in that, If the system is operating normally: If the DC system is in a normal operating state, the voltage divider sub-modules will be put into operation one by one at a predetermined rate.

9. The DC power dissipation device according to claim 6, characterized in that, When the DC line is in normal operation, it is necessary to perform voltage equalization operation on each voltage divider module in the energy consumption valve. During the voltage equalization operation, a fixed number of voltage divider modules with higher voltage are selected and disconnected.

10. The DC power dissipation device according to any one of claims 6-9, characterized in that, After the fault is recovered, all voltage divider submodules are locked.

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