Flexible distribution network fault rapid isolation control system and method

Abstract

The invention provides a flexible distribution network fault rapid isolation control system and method. In the system, the flexible distribution network fault rapid isolation control system can control the dual-active bridge converter and the rapid switch to be switched off when a DC side fault occurs, so that the energy consumption device and the power absorption circuit rapidly limit a fault current and avoid fault diffusion, thereby reducing the power failure time and range, improving the power supply reliability of the distribution network system, and improving the power supply reliability of the distribution network system. Meanwhile, through an energy consumption device and a power absorption circuit, excessive active power is absorbed, the frequency of a power distribution network system is kept stable, the problem that the power of the dual-active bridge type converter is excessive after a fault is solved, and safe and stable operation of the power distribution network system is ensured; faults of the power distribution network system are isolated through the energy consumption device and the power absorption circuit, and the construction cost of the power distribution network system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of distribution network, and in particular to a flexible distribution network fault rapid isolation control system and method. Background Art

[0002] The current distribution network is facing a new situation of high proportion of new energy access, large-scale promotion of electric vehicles and increasing proportion of DC load: it is expected that the proportion of new energy power generation will reach 50% in 2050; by 2025, there will be 2.3GW DC distribution network in the world, more than 50% of DC load will be DC or quasi-DC load, and most of the DC load will put forward higher requirements for the reliability and quality of power supply of distribution network. Under the above new situation, the current AC distribution network faces the following prominent problems: complex grid structure and increased short-circuit capacity; AC distribution and DC power consumption require multi-level AC / DC energy conversion, resulting in high loss; poor controllability and flexibility; poor support capacity of new energy power generation system for distribution network; a large number of power electronic devices and nonlinear loads lead to increased harmonic content and prominent power quality problems.

[0003] Compared with the traditional distribution network, flexible interconnected distribution is an important means to solve the above problems: by installing flexible intelligent switches at the traditional interconnection switches, the distribution network with traditional closed-loop design and open-loop operation is changed to flexible closed-loop operation, so that the distribution network has a faster response speed and stronger power flow regulation ability, and can realize the flexible interconnection of medium-voltage AC power grid and DC distribution system in the substation, effectively absorb renewable energy, reduce grid losses, optimize voltage distribution, and improve transient voltage stability. However, due to the technical characteristics and system configuration of flexible interconnected distribution, there are technical difficulties in fault isolation and clearance in flexible distribution networks that need to be solved urgently. The use of converters can achieve rapid isolation of faults, but this method will cause short-term power outages in the entire DC distribution network, reducing the reliability of power supply.

[0004] In addition, the DC circuit breaker is an effective fault isolation device, but when a DC fault occurs, there is no natural zero crossing point in the fault current, which makes it difficult to extinguish the arc. In addition, the inductive elements in the DC system store huge amounts of energy. Isolating the fault through a DC circuit breaker further increases the difficulty of clearing the DC fault. In addition, the manufacturing cost of the DC circuit breaker is high, which limits its widespread application in flexible distribution networks.

[0005] In recent years, several VSC (Voltagesource converter) topologies with DC fault ride-through capability have been proposed for flexible power transmission systems, among which full-bridge MMC (Modular multilevel converter) and hybrid sub-module modular multilevel converter can clear DC side fault current. Although these topologies have advantages such as improved efficiency and harmonics, they increase the number of sub-modules and hardware costs, which is also not conducive to the research and application of fault isolation and clearing functions of distribution network converters.

[0006] Although the above-mentioned prior art can isolate faults occurring in the distribution network system, it will also cause other more obvious defects to the distribution network system, such as reducing the power supply reliability of the distribution network system and increasing the construction cost of the distribution network system. Summary of the invention

[0007] In order to solve the technical problems existing in the prior art, the present invention provides a flexible distribution network fault rapid isolation control system and method.

[0008] The present invention provides a flexible distribution network fault rapid isolation control system, the flexible distribution network fault rapid isolation control system comprises: a dual active bridge converter, an energy consumption device, a fast switch and a power absorption circuit;

[0009] The positive output end of the dual-active bridge converter is connected to the first end of the energy consuming device, and the second end of the energy consuming device is respectively connected to the first end of the fast switch and the first end of the power absorbing circuit; the input end of the dual-active bridge converter is connected to the voltage source converter, and the negative output end of the dual-active bridge converter, the second end of the fast switch and the second end of the power absorbing circuit are connected to the DC power distribution network;

[0010] When a line fault occurs at the positive output end of the dual-active bridge converter, the dual-active bridge converter and the fast switch are controlled to be disconnected, and the energy stored in the dual-active bridge converter is consumed by the energy consumption device and the power absorption circuit. When the voltage and current of the DC bus in the DC distribution network are both zero, the dual-active bridge converter and the fast switch are controlled to be turned on.

[0011] Optionally, the dual-active bridge converter includes a plurality of conversion sub-modules, the input ends of the plurality of conversion sub-modules are connected in series, and the output ends of the plurality of conversion sub-modules are connected in parallel.

[0012] Optionally, it is characterized in that the conversion submodule includes a transformer, a primary full-bridge circuit and a secondary full-bridge circuit; the primary winding of the transformer is connected to the primary full-bridge circuit, and the secondary winding of the transformer is connected to the secondary full-bridge circuit;

[0013] The connection end of the primary full-bridge circuit serves as the input end of the conversion submodule, and the connection end of the secondary full-bridge circuit serves as the output end of the conversion submodule.

[0014] Optionally, the primary full-bridge circuit includes a first switch tube, a second switch tube, a third switch tube and a fourth switch tube;

[0015] The first switch tube and the second switch tube are connected in series to form a first bridge arm, the third switch tube and the fourth switch tube are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, the midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding of the transformer.

[0016] Optionally, the secondary full-bridge circuit includes a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube;

[0017] The fifth switch tube and the sixth switch tube are connected in series to form a third bridge arm, the seventh switch tube and the eighth switch tube are connected in series to form a fourth bridge arm, the third bridge arm and the fourth bridge arm are connected in parallel, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the transformer, and the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the transformer.

[0018] Optionally, the power absorption circuit includes a plurality of high-power resistors connected in series.

[0019] Optionally, the energy dissipation device includes a line resistor and an inductor connected in series.

[0020] Optionally, it further comprises a controller and a current sensor, wherein a first end of the current sensor is connected to the energy consumption device via a fast switch, and a second end of the current sensor is used to connect to the DC power distribution network; the controller is connected to the current sensor, the dual active bridge converter and the fast switch;

[0021] The controller is used to obtain the current output by the dual active bridge converter collected by the current sensor, and determine that a line fault occurs at the output end of the dual active bridge converter when the change rate of the output current of the dual active bridge converter is greater than a preset current change rate, and control the dual active bridge converter and the fast switch to be disconnected when a line fault occurs at the output end of the dual active bridge converter.

[0022] Optionally, the controller is further used to obtain the voltage and current of the DC bus in the DC distribution network, and control the dual active bridge converter and the fast switch to be turned on when the voltage and current of the DC bus in the DC distribution network are both zero.

[0023] Based on the same inventive concept, the present invention also provides a flexible distribution network fault rapid isolation control method, which is applicable to the flexible distribution network fault rapid isolation control system described above, and the method includes:

[0024] Obtaining the current output by the dual active bridge converter;

[0025] When the rate of change of the output current of the dual-active bridge converter is greater than a preset current change rate, determining that a line fault occurs at the output end of the dual-active bridge converter;

[0026] When a line fault occurs at the output end of the dual active bridge converter, the dual active bridge converter and the fast switch are controlled to be disconnected.

[0027] Optionally, when a line fault occurs at the output end of the dual-active bridge converter, after controlling the dual-active bridge converter and the fast switch to be disconnected, the method further includes:

[0028] Obtain the voltage and current of the DC bus in the DC distribution network;

[0029] When the voltage and current of the DC bus in the DC power distribution network are both zero, the dual active bridge converter and the fast switch are controlled to be turned on.

[0030] Based on the same inventive concept, the present invention also provides a computer device, including: one or more processors;

[0031] The processor is used to store one or more programs;

[0032] When the one or more programs are executed by the one or more processors, the flexible distribution network fault rapid isolation control method described above is implemented.

[0033] Based on the same inventive concept, the present invention also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, the flexible distribution network fault rapid isolation control method described above is implemented.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a flexible distribution network fault rapid isolation control system. In the system, the flexible distribution network fault rapid isolation control system can control the dual-active bridge converter and the fast switch to disconnect when a DC side fault occurs, so that the energy consumption device and the power absorption circuit can quickly limit the fault current and avoid the fault spreading, thereby reducing the power outage time and scope, improving the power supply reliability and safety of the distribution network system, effectively protecting the equipment from damage, and saving investment costs. At the same time, the energy consumption device and the power absorption circuit absorb excess active power, keep the frequency of the distribution network system stable, solve the problem of excess power of the dual-active bridge converter after the fault, ensure the safe and stable operation of the distribution network system, and isolate the fault of the distribution network system through the energy consumption device and the power absorption circuit, which is conducive to reducing the construction cost of the distribution network system.

[0036] The present invention also provides a flexible distribution network fault rapid isolation control method. The flexible distribution network fault rapid isolation control method can collect the current output by the dual active bridge converter by acquiring the current sensor, effectively determine the fault on the DC side, and quickly control the dual active bridge converter and the fast switch to disconnect, so that the energy consumption device and the power absorption circuit can quickly limit the fault current and avoid the fault spreading. Compared with the traditional fault handling method that relies on manual intervention, is complex to operate and inefficient, the flexible distribution network fault rapid isolation control method can automatically realize fault detection, isolation and recovery without manual intervention, simplifies the fault handling process, improves the efficiency and accuracy of fault handling, and can use flexible distribution networks of different scales and configurations, with good flexibility and scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of a flexible distribution network fault rapid isolation control system provided by the present invention;

[0038] Figure 2 A schematic diagram of a radial distribution network architecture provided by the present invention;

[0039] Figure 3 A schematic diagram of the connection between the positive temperature coefficient resistor and the fast switch provided by the present invention;

[0040] Figure 4 A topological diagram of a dual-active bridge converter provided by the present invention;

[0041] Figure 5 An equivalent circuit of a flexible distribution network fault rapid isolation control system provided by the present invention;

[0042] Figure 6 Another equivalent circuit of a flexible distribution network fault rapid isolation control system provided by the present invention;

[0043] Figure 7A schematic diagram of another flexible distribution network fault rapid isolation control system provided by the present invention;

[0044] Figure 8 A flowchart of a flexible distribution network fault rapid isolation control method provided by the present invention;

[0045] Fig. 9 A control flow chart of the fast switch provided by the present invention;

[0046] Fig.10 A flow chart of another flexible distribution network fault rapid isolation control method provided by the present invention;

[0047] Fig.11 A block diagram of a computer device provided by the present invention. DETAILED DESCRIPTION

[0048] Embodiment 1:

[0049] Figure 1 A schematic diagram of a flexible distribution network fault rapid isolation control system provided by the present invention, such as Figure 1 As shown, the flexible distribution network fault rapid isolation control system may include: a dual-active bridge converter 101, an energy consumption device, a fast switch Sa and a power absorption circuit 102; the positive output end of the dual-active bridge converter 101 is connected to the first end of the energy consumption device, and the second end of the energy consumption device is respectively connected to the first end of the fast switch Sa and the first end of the power absorption circuit 102; the input end of the dual-active bridge converter 101 is connected to the voltage source converter, and the negative output end of the dual-active bridge converter 101, the The second end of the fast switch Sa and the second end of the power absorption circuit 102 are connected to a DC power distribution network; when a line fault occurs at the positive output end of the dual-active bridge converter 101, the dual-active bridge converter 101 and the fast switch Sa are controlled to be disconnected, and the energy stored in the dual-active bridge converter 101 is consumed by the energy consumption device and the power absorption circuit 102. When the voltage and current of the DC bus in the DC power distribution network are both zero, the dual-active bridge converter 101 and the fast switch Sa are controlled to be turned on.

[0050] The power absorption circuit 102 includes a plurality of high-power resistors connected in series, and the high-power resistors may be PTCs (Positive Temperature Coefficient), heat dissipation resistors or power supply load resistors, etc. The energy dissipation device includes a line resistor R and an inductor L connected in series. The fast switch Sa is an automatic switch, for example, a BJT (Bipolar Junction Transistor), a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor) or a relay.

[0051] It should be noted that the flexible distribution network fault rapid isolation control system proposed in the present invention can be applied to Figure 2 The radial distribution network architecture shown in Figure 2 As shown, the radial distribution network architecture may include an AC grid, a VSC, a DAB (Dual active bridge converter) and a DC distribution network, and the DC distribution network may include a DC bus (Direct Current bus). In this architecture, the VSC rectifier, as the input stage of the distribution network system, converts the output voltage of the AC grid into DC power. The DAB, as the isolation stage, electrically isolates the medium / high voltage side from the low voltage side on the one hand, and reduces the DC voltage to meet the power supply voltage level requirements of the low voltage side on the other hand, and transmits it to the DC distribution network. The DC bus transmits the DC current output by the DAB to photovoltaic / energy storage, DC loads through a DC-DC converter, or transmits the DC current output by the DAB to an AC load through an inverter.

[0052] When the dual active bridge converter 101 and the fast switch Sa are controlled to be disconnected (i.e., the DC side fault is isolated), the power of DAB (i.e., the converter) will be excessive, and the power generation and load demand will lose balance, so a power absorption circuit 102 (virtual load) is required to keep its frequency within a stable range. Therefore, by installing a high-power resistor as the power absorption circuit 102 (virtual load) when the fault is close to the dual active bridge converter 101 (converter station), the power absorption circuit 102 is connected in parallel with the fast switch Sa (i.e., the fast mechanical switch), and by quickly inserting the power absorption circuit 102 (i.e., a high-power virtual load or virtual resistor) in the DC line, the fault current can be quickly limited, and the fault can be effectively prevented from spreading to the entire distribution network system, thereby significantly reducing the power outage time and range, and greatly improving the power supply reliability of the distribution network system. On the one hand, it limits the fault current to the range that the anti-parallel diode of the converter can withstand, and on the other hand, it keeps the frequency of the distribution network system stable by absorbing active power.

[0053] For example, Figure 3 As shown, Figure 3 The connection diagram of the positive temperature coefficient resistor and the fast switch provided by the present invention, in the normal operating state of the flexible distribution network fault fast isolation control system, the load current passes through path A, and the distribution network system operates normally. When a fault is detected, the flexible distribution network fault fast isolation control system switches the current to path B by disconnecting the fast switch Sa. The fast switch Sa is a fast mechanical switch. When a fault occurs, the arc voltage of 10 to 100V between the contacts of switch A will force the current to flow through path B. Path B is composed of several high-power positive temperature coefficient resistors in series, that is, a virtual load (or virtual resistor). When the current flows through several high-power positive temperature coefficient resistors in series, the high-power positive temperature coefficient resistors are heated, and the resistance of the high-power positive temperature coefficient resistors will increase to limit the fault current. By adding a virtual load (or virtual resistor) composed of several high-power positive temperature coefficient resistors in series in the DC line, the fault current can be quickly limited, and the fault can be effectively prevented from spreading to the entire distribution network, thereby significantly reducing the power outage time and range, and greatly improving the power supply reliability of the distribution network. At the same time, the combination of virtual load (or virtual resistor) and fast switch can replace the expensive DC circuit breaker, which significantly reduces the investment cost of the distribution network system. There is no need to carry out large-scale transformation or upgrade of the distribution network. The fault fast isolation function can be directly implemented on the existing system, reducing the complexity and maintenance difficulty of the system. At the same time, it can also adapt to the new trends of distribution network development such as new energy access and electric vehicle promotion, and meet the needs of future distribution network development.

[0054] In the present invention, the flexible distribution network fault rapid isolation control system does not use a DC circuit breaker. It isolates the DC side fault of the converter through a control strategy in conjunction with a fast switch Sa (i.e., a fast mechanical switch). When a line fault occurs at the positive output end of the dual-active bridge converter 101 (a DC side fault occurs in the distribution network system), the dual-active bridge converter 101 and the fast switch Sa are controlled to be disconnected, which can quickly limit the fault current and avoid the spread of the fault, thereby reducing the power outage time and range, improving the power supply reliability, effectively protecting the equipment from damage, and saving investment costs. At the same time, by installing a high-power resistor as a virtual load, absorbing excess active power, maintaining the stability of the system frequency, solving the problem of excess power in the converter station after the fault, and ensuring the safe and stable operation of the system.

[0055] Figure 4 A topological diagram of a dual-active bridge converter provided by the present invention is shown in Figure 4. The dual-active bridge converter 101 may include multiple conversion submodules, the input ends of the multiple conversion submodules are connected in series, and the output ends of the multiple conversion submodules are connected in parallel.

[0056] It should be noted that the two ends of the input terminals of multiple conversion submodules connected in series are connected to the DC side of MMC (Modular Multilevel Converter) as the input terminals of DAB, one end of the output terminals of multiple conversion submodules connected in parallel is connected to the DC distribution network as the positive output terminal of DAB through the line resistance R and inductance L, the other end of the output terminals of multiple conversion submodules connected in parallel is connected to the DC distribution network as the negative output terminal of DAB, and the AC end of MMC is connected to the AC (Alternating Current) bus. MMC is a special VSC topology.

[0057] For example, when a line grounding fault occurs at the output end of the dual active bridge converter 101 (a line grounding fault occurs on the DC side), the DC current begins to increase. When the DC current reaches twice the rated current, the fault is detected. Once the fault is detected, the MMC power reference value is set to zero, and all switches in the DAB converter are turned off. The energy stored in the DAB DC side capacitor is discharged through the inductor L (i.e., the DC side inductor) and the line resistance R (i.e., the overhead line resistance). At the end of this mode, the fault current reaches the maximum. The equivalent circuit of the flexible distribution network fault rapid isolation control system is as follows: Figure 5 When the DC bus voltage is zero, the energy stored in the DC inductor is discharged through the line resistance R (i.e., overhead transmission line resistance) and the anti-parallel diode in the DAB (i.e., converter). At this time, the equivalent circuit of the flexible distribution network fault rapid isolation control system is as follows: Figure 6When the DC current becomes zero, the fault can be isolated from the rest of the distribution network system by controlling the DAB and the fast switch Sa, and the anti-parallel diode and line resistance in the converter are used for discharge, which effectively utilizes the functions of existing equipment, reduces system complexity, and improves system reliability.

[0058] Optionally, Figure 4 As shown, the conversion submodule may include a transformer, a primary full-bridge circuit and a secondary full-bridge circuit; the primary winding of the transformer is connected to the primary full-bridge circuit, and the secondary winding of the transformer is connected to the secondary full-bridge circuit.

[0059] The connection end of the primary full-bridge circuit serves as the input end of the conversion submodule, and the connection end of the secondary full-bridge circuit serves as the output end of the conversion submodule.

[0060] It should be noted that the primary full-bridge circuit can be an inverter circuit, and the secondary full-bridge circuit can be a rectifier circuit. The primary full-bridge circuit converts the DC current in the input conversion submodule into AC current, and transmits the AC current to the transformer. The transformer can transmit the AC current to the secondary full-bridge circuit through the primary winding and the secondary winding, and adjust the output AC current through the coil turns ratio of the primary winding and the secondary winding, and control the DC current output by the secondary full-bridge circuit, so that the conversion submodule converts the medium / high voltage current into a low voltage current.

[0061] Optionally, Figure 4 As shown, the primary full-bridge circuit includes a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; the first switch tube and the second switch tube are connected in series to form a first bridge arm, the third switch tube and the fourth switch tube are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, the midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding of the transformer.

[0062] Among them, the first switch tube, the second switch tube, the third switch tube and the fourth switch tube can be MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), BJT (Bipolar Junction Transistor) or IGBT (Insulated Gate Bipolar Transistor).

[0063] Optionally, Figure 4As shown, the secondary full-bridge circuit includes a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube; the fifth switch tube and the sixth switch tube are connected in series to form a third bridge arm, the seventh switch tube and the eighth switch tube are connected in series to form a fourth bridge arm, the third bridge arm and the fourth bridge arm are connected in parallel, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the transformer, and the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the transformer.

[0064] Among them, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube can be MOSFET, BJT or IGBT.

[0065] Figure 7 A schematic diagram of another flexible distribution network fault rapid isolation control system provided by the present invention, the flexible distribution network fault rapid isolation control system may also include a controller 103 and a current sensor 104, the first end of the current sensor 104 is connected to the energy consumption device through a fast switch Sa, and the second end of the current sensor 104 is used to connect to the DC distribution network; the controller 103 is connected to the current sensor 104, the dual-active bridge converter 101 and the fast switch Sa; the controller 103 is used to obtain the current output by the dual-active bridge converter 101 collected by the current sensor 104, and when the change rate of the output current of the dual-active bridge converter 101 is greater than a preset current change rate, it is determined that a line fault occurs at the output end of the dual-active bridge converter 101, and when a line fault occurs at the output end of the dual-active bridge converter 101, the dual-active bridge converter 101 and the fast switch Sa are controlled to be disconnected.

[0066] Among them, the current sensor 104 can be a Hall sensor (including a closed-loop Hall sensor or an open-loop Hall sensor), a resistor shunt or a current transformer, etc. The controller 103 can be a DSP (Digital Signal Processor), a CPU controller 103 or a microprogram controller 103, etc. The preset current change rate can be the maximum value of the change rate of the output current of the dual-active bridge converter 101 when the flexible distribution network fault rapid isolation control system is operating normally.

[0067] It should be noted that the first end of the current sensor 104 can be connected to the fast switch Sa and the power absorption circuit 102, and the second end of the current sensor 104 can be connected to the DC distribution network. The current sensor 104 collects the current output by the dual-active bridge converter 101 and sends the collected current to the controller 103. When the controller 103 receives the current collected by the current sensor 104, it calculates the change rate of the output current of the dual-active bridge converter 101, and judges whether a line fault occurs at the output end of the dual-active bridge converter 101 through the change rate of the output current of the dual-active bridge converter 101. When the change rate of the output current of the dual-active bridge converter 101 is greater than the preset current change rate, it is determined that a fault occurs.

[0068] For example, the closed-loop Hall sensor detects the current output by the dual-active bridge converter 101 (i.e., the current on the DC side), and the controller 103 receives the current detected by the Hall current sensor 104, and calculates the current change rate di / dt (the current change per unit time) through the detected current. The maximum value of the current change rate during normal operation of the flexible distribution network fault rapid isolation control system can be set to a preset current change rate (i.e., a detection threshold). When the detected current change rate is greater than the preset current change rate (i.e., the detection threshold), it is determined that a fault has occurred. When the controller 103 determines that a fault has occurred, it sends a signal to the DAB to disconnect the IGBT.

[0069] Optionally, the controller 103 is further configured to obtain a voltage and a current of a DC bus in the DC distribution network, and control the dual active bridge converter 101 and the fast switch Sa to be turned on when the voltage and the current of the DC bus in the DC distribution network are both zero.

[0070] It should be noted that the controller 103 can also be connected to the VSC. When the voltage and current of the DC bus in the DC distribution network are both zero, it can be determined that the fault is eliminated. After the fault is eliminated, the controller 103 can first send a drive signal to the switch tube of the DAB converter, and the switch tube of the DAB converter is closed, so that the voltage of the DAB converter rises to a preset voltage reference value. When the voltage of the DAB converter reaches the preset voltage reference value, the reference power of the VSC is set to the value before the fault.

[0071] Embodiment 2:

[0072] Based on the same inventive concept, the present invention also provides a flexible distribution network fault rapid isolation control method, which is applicable to the flexible distribution network fault rapid isolation control system described in the above embodiment. Figure 8 As shown, the method comprises the following steps:

[0073] In step 801, the current output by the dual active bridge converter is obtained.

[0074] In this step, the current output by the dual active bridge converter can be obtained by collecting the current output by the dual active bridge converter through a current sensor provided in the flexible distribution network fault rapid isolation control system.

[0075] In step 802, when the rate of change of the output current of the dual active bridge converter is greater than a preset current change rate, it is determined that a line fault occurs at the output end of the dual active bridge converter.

[0076] The preset current change rate may be a maximum value of the change rate of the output current of the dual-active bridge converter when the flexible distribution network fault rapid isolation control system operates normally.

[0077] For example, Fig. 9 As shown, the first step of the control strategy may be: a DC side fault is detected, that is, when the rate of change of the output current of the dual active bridge converter is greater than a preset current change rate, the flexible distribution network fault rapid isolation control system detects that there is a fault on the DC side.

[0078] It should be noted that the rate of change of the output current of the dual active bridge converter is calculated by the current output by the dual active bridge converter. When the rate of change of the output current of the dual active bridge converter is greater than the preset current change rate, it is determined that a line fault (i.e., a DC side fault) occurs at the output end of the dual active bridge converter. The method for determining the rate of change of the output current of the dual active bridge converter may include: taking the current output by the dual active bridge converter currently obtained as the current current, taking the current output by the dual active bridge converter corresponding to the preset time interval as the historical current, determining the current difference between the current current and the historical current, and taking the ratio of the current difference to the preset time interval as the rate of change of the output current of the dual active bridge converter. The method for determining the rate of change of the output current of the dual active bridge converter may also be other methods of the prior art, which will not be described in detail in the present invention.

[0079] In step 803, when a line fault occurs at the output end of the dual active bridge converter, the dual active bridge converter and the fast switch are controlled to be disconnected.

[0080] It should be noted that when a line fault occurs at the output end of the dual-active bridge converter, the dual-active bridge converter and the fast switch can be controlled to disconnect by sending a drive signal to the dual-active bridge converter and the fast switch, wherein the drive signal can be a voltage signal, a PWM (Pulse Width Modulation) signal, a current signal, a digital signal or a frequency signal, etc.

[0081] For example, Fig. 9As shown in FIG. 1 , the second step of the control strategy can be: turn off all IGBTs in the DAB, that is, when a DC side fault is detected, turn off all insulated gate bipolar transistors (IGBTs) in the DAB, and the energy stored in the DAB DC side capacitor is released through the DC side inductance and line resistance. The equivalent circuit is shown in FIG. Figure 5 shown.

[0082] In the present invention, the flexible distribution network fault rapid isolation control method can collect the current output by the dual active bridge converter by acquiring the current sensor, effectively determine the fault on the DC side, and quickly control the dual active bridge converter and the fast switch to disconnect, so that the energy consumption device and the power absorption circuit can quickly limit the fault current and avoid the spread of the fault. Compared with the traditional fault handling method of manual intervention, which is complicated and inefficient, the flexible distribution network fault rapid isolation control method can automatically realize the detection, isolation and recovery of the fault without manual intervention, simplifying the fault handling process, improving the efficiency and accuracy of fault handling, and can use flexible distribution networks of different scales and configurations, with good flexibility and scalability. At the same time, it can also adapt to the new trends of distribution network development such as new energy access and electric vehicle promotion, and meet the needs of future distribution network development.

[0083] Optionally, when a line fault occurs at the output end of the dual active bridge converter, after the dual active bridge converter and the fast switch are controlled to be disconnected, as follows Fig.10 As shown, the method may further include the following steps:

[0084] In step 804, the voltage and current of the DC bus in the DC distribution network are obtained.

[0085] In this step, the voltage and current of the DC bus in the DC distribution network can be obtained by setting a voltage detection device and a current detection device on the DC bus of the DC distribution network. The voltage detection device can be a capacitive voltage sensor, a resistive voltage sensor, a Hall effect voltage sensor, or a photoelectric isolation voltage sensor, etc., and the current detection device can be a Hall sensor (including a closed-loop Hall sensor or an open-loop Hall sensor), a resistor shunt, or a current transformer, etc.

[0086] For example, Fig. 9 As shown, the third step of the control strategy can be: determine U dc =0? : Check whether the DC side voltage Udc is zero. When the DC side voltage Udc is not zero, Figure 5 The equivalent circuit shown in FIG. 1 releases the energy stored in the DAB DC link capacitor. When the DC link voltage Udc is detected to be zero, Figure 6 The equivalent circuit shown is to discharge through the anti-parallel diode and the power absorption circuit, and judge I dc=0? : Detect the DC side current I dc Is it zero? dc When it is not zero, Figure 6 The equivalent circuit discharge is shown.

[0087] In step 805, when the voltage and current of the DC bus in the DC distribution network are both zero, the dual active bridge converter and the fast switch are controlled to be turned on.

[0088] It should be noted that when the voltage and current of the DC bus in the DC distribution network are both zero, it can be determined that the fault has been eliminated. After the fault has been eliminated, a driving signal can be sent to the switch tube and the fast switch of the DAB converter to control the switch tube and the fast switch of the DAB converter to close, so that the voltage of the DAB converter rises to a preset voltage reference value.

[0089] For example, Fig. 9 As shown, the fourth step of the control strategy can be: enable the switch signal of the IGBT in the DAB and restore: when the voltage and current of the DC bus in the DC distribution network are both zero (i.e., confirm that the current is lower than the safety threshold), control the dual active bridge converter (i.e., re-enable the switch signal of the IGBT in the DAB) and the fast switch to turn on, and the distribution network system returns to a normal working state. After enabling the switch signal of the IGBT in the DAB and restoring, the execution of this control strategy ends.

[0090] Embodiment 3:

[0091] Based on the same inventive concept, the present invention also provides a computer device, such as Fig.11 As shown, the computer device includes a processor and a memory, the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits, or other processors.

[0092] (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate array (Field-Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in a computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of a flexible distribution network fault rapid isolation control method in the above-mentioned embodiment.

[0093] Embodiment 4:

[0094] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in a computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of a flexible distribution network fault rapid isolation control method in the above embodiment.

[0095] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0096] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0097] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0098] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0099] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A flexible distribution network fault rapid isolation control system, characterized in that: The flexible distribution network fault rapid isolation control system comprises: a dual active bridge converter, an energy dissipation device, a fast switch and a power absorption circuit; The positive output end of the dual-active bridge converter is connected to the first end of the energy consuming device, and the second end of the energy consuming device is respectively connected to the first end of the fast switch and the first end of the power absorbing circuit; the input end of the dual-active bridge converter is connected to the voltage source converter, and the negative output end of the dual-active bridge converter, the second end of the fast switch and the second end of the power absorbing circuit are connected to the DC power distribution network; When a line fault occurs at the positive output end of the dual-active bridge converter, the dual-active bridge converter and the fast switch are controlled to be disconnected, and the energy stored in the dual-active bridge converter is consumed by the energy consumption device and the power absorption circuit. When the voltage and current of the DC bus in the DC distribution network are both zero, the dual-active bridge converter and the fast switch are controlled to be turned on.

2. The flexible distribution network fault rapid isolation control system according to claim 1 is characterized in that: The dual-active bridge converter comprises a plurality of conversion submodules, the input ends of the plurality of conversion submodules are connected in series, and the output ends of the plurality of conversion submodules are connected in parallel.

3. The flexible distribution network fault rapid isolation control system according to claim 2 is characterized in that: The conversion submodule includes a transformer, a primary full-bridge circuit and a secondary full-bridge circuit; the primary winding of the transformer is connected to the primary full-bridge circuit, and the secondary winding of the transformer is connected to the secondary full-bridge circuit; The connection end of the primary full-bridge circuit serves as the input end of the conversion submodule, and the connection end of the secondary full-bridge circuit serves as the output end of the conversion submodule.

4. The flexible distribution network fault rapid isolation control system according to claim 3 is characterized in that: The primary full-bridge circuit includes a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; The first switch tube and the second switch tube are connected in series to form a first bridge arm, the third switch tube and the fourth switch tube are connected in series to form a second bridge arm, the first bridge arm and the second bridge arm are connected in parallel, the midpoint of the first bridge arm is connected to the first end of the primary winding of the transformer, and the midpoint of the second bridge arm is connected to the second end of the primary winding of the transformer.

5. The flexible distribution network fault rapid isolation control system according to claim 4 is characterized in that: The secondary full-bridge circuit includes a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube; The fifth switch tube and the sixth switch tube are connected in series to form a third bridge arm, the seventh switch tube and the eighth switch tube are connected in series to form a fourth bridge arm, the third bridge arm and the fourth bridge arm are connected in parallel, the midpoint of the third bridge arm is connected to the first end of the secondary winding of the transformer, and the midpoint of the fourth bridge arm is connected to the second end of the secondary winding of the transformer.

6. The flexible distribution network fault rapid isolation control system according to claim 1, characterized in that: The power absorption circuit includes a plurality of high power resistors connected in series.

7. The flexible distribution network fault rapid isolation control system according to claim 1, characterized in that: The energy dissipation device includes a line resistor and an inductor connected in series.

8. The flexible distribution network fault rapid isolation control system according to claim 1, characterized in that: It also includes a controller and a current sensor, wherein a first end of the current sensor is connected to the energy consumption device through a fast switch, and a second end of the current sensor is used to connect to the DC power distribution network; the controller is connected to the current sensor, the dual active bridge converter and the fast switch; The controller is used to obtain the current output by the dual active bridge converter collected by the current sensor, and determine that a line fault occurs at the output end of the dual active bridge converter when the change rate of the output current of the dual active bridge converter is greater than a preset current change rate, and control the dual active bridge converter and the fast switch to be disconnected when a line fault occurs at the output end of the dual active bridge converter.

9. The flexible distribution network fault rapid isolation control system according to claim 8, characterized in that: The controller is further used to obtain the voltage and current of the DC bus in the DC distribution network, and control the dual active bridge converter and the fast switch to be turned on when the voltage and current of the DC bus in the DC distribution network are both zero.

10. A method for rapid isolation control of flexible distribution network faults, characterized in that: Applicable to the flexible distribution network fault rapid isolation control system according to any one of claims 1 to 9 above, the method comprising: Obtaining the current output by the dual active bridge converter; When the rate of change of the output current of the dual-active bridge converter is greater than a preset current change rate, determining that a line fault occurs at the output end of the dual-active bridge converter; When a line fault occurs at the output end of the dual active bridge converter, the dual active bridge converter and the fast switch are controlled to be disconnected.

11. The flexible distribution network fault rapid isolation control method according to claim 10, characterized in that: When a line fault occurs at the output end of the dual active bridge converter, after controlling the dual active bridge converter and the fast switch to be disconnected, the method further includes: Obtain the voltage and current of the DC bus in the DC distribution network; When the voltage and current of the DC bus in the DC power distribution network are both zero, the dual active bridge converter and the fast switch are controlled to be turned on.

Images