Blocking device of direct current power distribution system

Abstract

The invention relates to a blocking device of a direct-current power distribution system, and belongs to the technical field of direct-current power distribution. Comprising a blocking module and a control module. The blocking module comprises a two-quadrant DC / DC converter, two ends of a branch in which a first power device and a second power device are connected in series in the two-quadrant DC / DC converter are used for connecting a power supply end of the DC power distribution system, and two ends of the second power device are used for connecting a load end of the DC power distribution system; the control module is used for judging whether a short-circuit fault occurs or not and controlling the first power device to be turned off if the current flowing through the direct-current power distribution system is greater than a blocking current constant value under the condition that the short-circuit fault is judged; on the contrary, current closed-loop control is carried out according to the difference between the current flowing through the direct-current power distribution system and the blocking current constant value so as to control on and off of the first power device; the blocking current constant value is smaller than or equal to the maximum withstand current of the load end of the direct-current power distribution system, and the current of the direct-current power distribution system under current closed-loop control meets the triggering condition of differential protection.

Description

Technical Field

[0001] The present invention relates to a blocking device for a DC power distribution system, belonging to the technical field of DC power distribution. Background Art

[0002] According to the national plan, by 2030, remarkable results will be achieved in the comprehensive green transformation of economic and social development, and the energy utilization efficiency of key energy-consuming industries will reach the international advanced level. By 2060, a complete economic system featuring green, low-carbon and circular development and a clean, low-carbon, safe and efficient energy system will be established, the energy utilization efficiency will reach the international advanced level, and the proportion of non-fossil energy consumption will exceed 80%. Centering on the overall goal of building a new energy system and a new power system, a new power distribution system that is safe, efficient, clean, low-carbon, flexible, and intelligent will be created, which puts forward higher requirements for the protection performance of the power system. It is necessary to quickly isolate and locate faults. Therefore, when a fault occurs in the power distribution system, regardless of the operating mode, fault type, and fault location of the power distribution system, the relay protection device needs to have sensitive protection, reliable operation, and no misoperation functions, which poses stricter requirements for the relay protection device.

[0003] The DC power distribution system generally operates without grounding. There are many DC power sources in parallel and the lines are long. When a grounding or short-circuit fault occurs in the DC power distribution system, due to the small impedance of the DC power distribution system and the fast rising speed of the current, the current can usually rise to a very large value in a few microseconds, which is sufficient to damage the load of the DC power distribution system. However, the detection of differential protection of the existing relay protection device is in milliseconds, that is, it usually takes at least a few milliseconds to complete the detection of differential protection. When a grounding or short-circuit occurs in the DC system, the differential protection has not detected the fault, and the short-circuit current may have increased rapidly, resulting in the load at the load end being impacted by the large short-circuit current, thus causing an accident. Therefore, it is difficult for the differential protection in the existing relay protection device to timely protect and locate the grounding or short-circuit fault of the DC power distribution system, resulting in easy occurrence of accidents. Summary of the Invention

[0004] The purpose of the present invention is to provide a blocking device for a DC power distribution system to solve the problem that the existing differential protection is difficult to timely protect and locate the grounding or short-circuit fault of the DC power distribution system, resulting in easy occurrence of accidents.

[0005] The present invention provides a blocking device for a DC power distribution system to solve the above technical problems. The blocking device of the DC power distribution system includes a control module and a blocking module. The blocking module includes a two-quadrant DC / DC converter. The two ends of the branch in which a first power device and a second power device are connected in series in the converter are used to connect to the power supply end of the DC power distribution system, and the two ends of the second power device are used to connect to the load end of the DC power distribution system. The control module is used to determine whether there is a short-circuit fault in the DC power distribution system. When a short-circuit fault is determined, if the current of the DC power distribution system is greater than the blocking current setting value, the first power device is controlled to turn off. Otherwise, current closed-loop control is performed according to the difference between the current of the DC power distribution system and the blocking current setting value, so as to control the turning on and off of the first power device according to the control quantity output by the current closed-loop control. The blocking current setting value is less than the maximum withstand current of the load end of the DC power distribution system, and the current of the DC power distribution system under current closed-loop control satisfies the triggering condition of differential protection.

[0006] Further, the control module is further used to perform voltage closed-loop control according to the difference between the real-time voltages of the power supply end and the load end of the DC power distribution system when it is determined that there is no short-circuit fault in the DC power distribution system, so as to control the turning on and off of the first power device according to the control quantity output by the voltage closed-loop control.

[0007] Further, an RCD buffer circuit is also included in the blocking module and is connected in parallel across the two ends of the first power device in the two-quadrant DC / DC converter.

[0008] Further, a capacitor is also included in the blocking module and is connected in parallel across the two ends of the branch in which the first power device and the second power device in the two-quadrant DC / DC converter are connected in series.

[0009] Further, an inductor is also included in the blocking module and is connected in series in the line for connecting the two ends of the second power device to the load end of the DC power distribution system.

[0010] Further, a Hall detector is also connected in series in the line where the inductor is located. The Hall detector is used to detect the current in the line where it is located. The method for determining whether there is a short-circuit fault in the DC power distribution system includes: determining whether the current detected by the Hall detector is greater than the set current value. If it is greater, it is determined that a short-circuit fault has occurred in the DC power distribution system.

[0011] Further, the method for determining whether there is a short-circuit fault in the DC power distribution system includes: determining the change rate of the current flowing through the first power device in the two-quadrant DC / DC converter according to the voltage change amount of the first power device and the inductor within the set time. If the change rate of the current flowing through the first power device in the two-quadrant DC / DC converter is greater than the set current change rate, it is determined that a short-circuit fault has occurred in the DC power distribution system.

[0012] Further, the lower threshold value of the blocking current setting value ranges from 1.2 times to 10 times the rated current of the load at the load end of the DC power distribution system, so that the current in the DC power distribution system under current closed-loop control meets the triggering conditions of differential protection.

[0013] Further, the blocking module in the blocking device of the DC power distribution system further includes a first circuit breaker and a second circuit breaker; a branch of the first power device and the second power device connected in series in the two-quadrant DC / DC converter in the blocking module of the blocking device of the DC power distribution system is connected to the power supply end of the DC power distribution system through the first circuit breaker, and both ends of the second power device are connected to the load end of the DC power distribution system through the second circuit breaker.

[0014] Beneficial effects: The present invention provides a new blocking device for a DC power distribution system. When the control module in the blocking device determines that a short - circuit fault has occurred in the DC power distribution system, if the current flowing through the DC power distribution system is greater than the blocking current setting value (the blocking current setting value is less than the maximum withstand current at the load end of the DC power distribution system and greater than the current setting value trigger condition that enables the current in the DC power distribution system under current closed - loop control to trigger the differential protection action), the control module controls the first power device in the two - quadrant DC / DC converter in the blocking module for accessing the DC power distribution system to turn off. Conversely, according to the difference between the current flowing through the DC power distribution system and the blocking current setting value, current closed - loop control is performed to control the turning on and off of the first power device based on the control quantity output by the current closed - loop control. By controlling the conduction and turning off of the first power device (the response speed of the power device is faster than that of the mechanical switch, and the turning - off control of the power device is used to quickly suppress the short - circuit current, which can greatly improve the safety of the DC power supply system) in the two - quadrant DC / DC converter in the blocking module through the control module in the blocking device, when the control module determines that a short - circuit fault has occurred in the DC power distribution system, it controls the current flowing through the DC power distribution system to be as close as possible to the blocking current setting value and not exceed the blocking current setting value. Based on the fact that the blocking current setting value is set to be less than the maximum withstand current at the load end of the DC power distribution system, the short - circuit current is limited below the maximum withstand current at the load end of the DC power distribution system, avoiding the impact of the short - circuit current generated by the short - circuit fault on the load end of the DC power distribution system and ensuring the safety of the DC power supply system during the triggering of the differential protection action. At the same time, although the conduction and turning off of the power device suppress the short - circuit current to a certain extent, the current in the DC power distribution system under current closed - loop control still satisfies the triggering condition of the differential protection, that is, the current in the DC power distribution system after being suppressed by the current closed - loop control can still trigger the differential protection action. Coupled with the above - mentioned rapid suppression of the short - circuit current, it is ensured that after a short - circuit fault occurs in the DC power distribution system, the DC power supply system can safely enter the differential protection detection stage and successfully trigger the differential protection action after the differential protection detection is completed, thereby realizing the positioning of the short - circuit fault. Brief Description of the Drawings

[0015] Figure 1 It is the structural schematic diagram of the blocking module in the blocking device in the embodiment of the blocking device for the DC power distribution system of the present invention;

[0016] Figure 2 It is the principle example diagram of the control module in the embodiment of the blocking device for the DC power distribution system of the present invention. Detailed Embodiments

[0017] The following further describes the specific embodiments of the present invention with reference to the drawings.

[0018] Embodiment of the blocking device for a DC power distribution system

[0019] This embodiment provides a technical solution for a blocking device of a DC power distribution system. When the control module in the blocking device determines that a short - circuit fault has occurred, by controlling the conduction and turn - off of the first power device in the two - quadrant DC / DC converter in the blocking module connected to the DC power distribution system, the current flowing through the DC power distribution system does not exceed the blocking current setting value. The blocking current setting value is less than the maximum withstand current of the load end of the DC power distribution system, and the current in the DC power distribution system under current closed - loop control satisfies the triggering condition of differential protection, avoiding the impact of the short - circuit current generated by the short - circuit fault on the load end of the DC power distribution system. At the same time, after a short - circuit fault occurs in the DC power distribution system, it can safely enter the differential protection detection stage, and trigger the differential protection action after the differential protection detection is completed, realizing the location of the short - circuit fault.

[0020] The blocking device of the DC power distribution system specifically includes a control module and a blocking module. The blocking module includes a two - quadrant DC / DC converter. The two ends of the branch in which the first power device and the second power device are connected in series in the converter are used to connect to the power supply end of the DC power distribution system, and the two ends of the second power device are used to connect to the load end of the DC power distribution system. The control module is used to determine whether a short - circuit fault occurs in the DC power distribution system. When a short - circuit fault is determined, if the current in the DC power distribution system is greater than the blocking current setting value, the control module controls the first power device to turn off; otherwise, it performs current closed - loop control according to the difference between the current in the DC power distribution system and the blocking current setting value, and controls the turn - on and turn - off of the first power device according to the control quantity output by the current closed - loop control. The blocking current setting value is less than the maximum withstand current of the load end of the DC power distribution system, and the current in the DC power distribution system under current closed - loop control satisfies the triggering condition of differential protection.

[0021] When the control module in the blocking device of the DC power distribution system determines that a short - circuit fault has occurred, by controlling the conduction and turn - off of the first power device in the two - quadrant DC / DC converter in the blocking module connected to the DC power distribution system, the current flowing through the DC power distribution system does not exceed the blocking current setting value. The blocking current setting value is less than the maximum withstand current of the load end of the DC power distribution system, and the current in the DC power distribution system under current closed - loop control satisfies the triggering condition of differential protection, avoiding the impact of the short - circuit current generated by the short - circuit fault on the load end of the DC power distribution system, ensuring the safety of the DC power supply system from the occurrence of a short - circuit fault to the triggering of the differential protection action, enabling the DC power supply system to safely enter the differential protection detection stage, and triggering the differential protection action after the differential protection detection is completed, realizing the location of the short - circuit fault.

[0022] The following is a specific example of the blocking device for the DC power distribution system:

[0023] The blocking device for the DC power distribution system includes a blocking module for accessing the DC power distribution system; the structural schematic diagram of the blocking module in this blocking device is as shown in Figure 1 In the figure, the blocking module includes a two - quadrant DC / DC converter. In the two - quadrant DC / DC converter, the two ends of the branch in which the first power device and the second power device are connected in series are used to connect to the power supply end of the DC power distribution system, and the two ends of the second power device are used to connect to the load end of the DC power distribution system; the first power device corresponds to T1 in Figure 1 and the second power device corresponds to T2 in Figure 1 In this embodiment, the first power device and the second power device are IGBTs. In other embodiments, at least one of the first power device and the second power device can also be other fully - controlled power devices, such as IGCTs; and, in this embodiment, the second power device is in the off state;

[0024] In this embodiment, the blocking module also includes an RCD snubber circuit connected in parallel across the two ends of the first power device in the two - quadrant DC / DC converter. The resistor in the RCD snubber circuit corresponds to R in Figure 1 the capacitor in the RCD snubber circuit corresponds to C in Figure 1 and the diode in the RCD snubber circuit corresponds to D in Figure 1 This RCD snubber circuit is mainly used to suppress the voltage and the rate of voltage change across the two ends of the first power device in the two - quadrant DC / DC converter.

[0025] In this embodiment, the blocking module also includes a capacitor (this capacitor corresponds to C in Figure 1 ) connected in parallel across the two ends of the branch in which the first power device and the second power device in the two - quadrant DC / DC converter are connected in series. This capacitor C is mainly used for energy interaction.

[0026] In this embodiment, the blocking module also includes an inductor (the inductor corresponds to L in Figure 1 ) connected in series on the line connecting the two ends of the second power device to the load end of the DC power distribution system. This inductor is mainly used to suppress the rate of rise of the current flowing through the first power device in the two - quadrant DC / DC converter.

[0027] In this embodiment, the blocking module in the blocking device of the DC power distribution system further includes a first circuit breaker QF1 and a second circuit breaker QF2; the two circuit breakers QF1 and QF2 are used to connect the blocking module in the blocking device of the DC power distribution system to the DC power distribution system; both ends of the branch in the two-quadrant DC / DC converter in the blocking module of the DC power distribution system, where a first power device and a second power device are connected in series, are connected to the power supply end of the DC power distribution system through QF1, and both ends of the second power device are connected to the load end of the DC power distribution system through QF2; in other embodiments, both ends of the branch in the two-quadrant DC / DC converter in the blocking module of the DC power distribution system, where a first power device and a second power device are connected in series, can also be connected to the power supply end of the DC power distribution system through other connection devices; both ends of the second power device can also be connected to the load end of the DC power distribution system through other connection devices; or, both ends of the branch in the two-quadrant DC / DC converter in the blocking module of the DC power distribution system, where a first power device and a second power device are connected in series, are directly connected to the power supply end of the DC power distribution system; it is also possible that both ends of the second power device are directly connected to the load end of the DC power distribution system.

[0028] The blocking device of the DC power distribution system further includes a control module; a schematic diagram of the principle of the control module is as Figure 2 shown. The hardware for implementing control of the control module (corresponding to the control system in Figure 2 ) may include a DSP chip, an ARM processor, and an FPGA programmable logic device (other hardware devices or software architectures may also be used in other embodiments). The control module is used to determine whether a short-circuit fault occurs in the DC power distribution system (where the short-circuit faults that can be determined here include short-circuit faults and grounding faults in the internal lines of the DC power distribution system). And in the case where it is determined that a short-circuit fault has occurred, if the current flowing through the DC power distribution system is greater than the blocking current setting value, the first power device in the two-quadrant DC / DC converter is controlled to be forcibly turned off. Specifically, the first power device is turned off by applying a low-level pulse (in this embodiment, the pulse is the Figure 2 PWM pulse in Figure 2 ). Conversely, current closed-loop control is performed according to the difference between the current flowing through the DC power distribution system (the current flowing through the DC power distribution system corresponds to the DC current Idc in Figure 2 ) and the blocking current setting value, so as to control the turning on and off of the first power device according to the control quantity output by the current closed-loop control; specifically, the method of controlling the turning on and off of the first power device according to the control quantity output by the current closed-loop control can be: applying a corresponding pulse to the first power device according to the control quantity output by the current closed-loop control (in this embodiment, this pulse is the Figure 2The PWM pulses therein can control the turn-on and turn-off of the first power device by obtaining corresponding PWM pulses through the control quantity output by current closed-loop control according to the EPWM pulse generation principle. In this embodiment, PI control is adopted for current closed-loop control.

[0029] Considering that the blocking current setting value is less than the maximum withstand current at the load end of the DC power distribution system and enabling the current in the DC power distribution system under current closed-loop control to meet the triggering condition of differential protection, in this embodiment, the lower threshold value range of the blocking current setting value is 1.2 times to 10 times the rated current of the load at the load end of the DC power distribution system, so that the current in the DC power distribution system under current closed-loop control meets the triggering condition of differential protection. The control module is further configured to, when it is determined that the DC power distribution system has not failed, perform voltage closed-loop control according to the difference between the real-time voltages of the power supply end and the load end of the DC power distribution system (the real-time voltage of the power supply end corresponds to the bus voltage Udc1 therein, and the real-time voltage of the load corresponds to the bus voltage Udc2 therein), and control the turn-on and turn-off of the first power device according to the control quantity output by the voltage closed-loop control. When the DC power distribution system has not failed, this blocking device can ensure that the DC power supply system connected with this blocking device can still operate stably. In addition, it can also make the voltages at both ends of the DC power supply system more consistent and improve the voltage stability of the DC power supply system. Figure 2 corresponds to the bus voltage Udc1 therein, and the real-time voltage of the load corresponds to Figure 2 the bus voltage Udc2 therein), and perform voltage closed-loop control according to the difference therebetween, and control the turn-on and turn-off of the first power device according to the control quantity output by the voltage closed-loop control. When the DC power distribution system has not failed, this blocking device can ensure that the DC power supply system connected with this blocking device can still operate stably. In addition, it can also make the voltages at both ends of the DC power supply system more consistent and improve the voltage stability of the DC power supply system.

[0030] In this embodiment, a Hall detector is also connected in series on the line where the inductor is located (the Hall detector corresponds to A therein), and the Hall detector is used to detect the current on the line where it is located. The specific method for the control module to determine whether the DC power distribution system has a short-circuit fault is: determine whether the current detected by the Hall detector is greater than the set current value. If it is greater, it is determined that the DC power distribution system has a short-circuit fault. Figure 1 corresponds to A therein), and the Hall detector is used to detect the current on the line where it is located. The specific method for the control module to determine whether the DC power distribution system has a short-circuit fault is: determine whether the current detected by the Hall detector is greater than the set current value. If it is greater, it is determined that the DC power distribution system has a short-circuit fault.

[0031] In other embodiments, the method for the control module to determine whether the DC power distribution system has a short-circuit fault can also be: according to the voltage change amount of the first power device in the two-quadrant DC / DC converter and the inductor within a set time, determine the current change rate flowing through the first power device in the two-quadrant DC / DC converter. If the current change rate flowing through the first power device in the two-quadrant DC / DC converter is greater than the set current change rate, it is determined that the DC power distribution system has a short-circuit fault. The specific method for determining the current change rate flowing through the first power device in the two-quadrant DC / DC converter according to the voltage change amount of the first power device at both ends and the inductor within a set time is to determine the current change rate flowing through the first power device in the two-quadrant DC / DC converter according to the ratio of the voltage change amount of the first power device at both ends and the inductor within a set time.

[0032] The formula for determining the rate of change of the current flowing through the first power device in a two - quadrant DC / DC converter is as follows:

[0033]

[0034] In the formula, is the rate of change of the current flowing through the first power device in the two - quadrant DC / DC converter, △t is the set time, △i is the current flowing through the first power device in the two - quadrant DC / DC converter, △U is the change in voltage across the first power device within the set time, and L is the inductor;

[0035] This method of determining whether a short - circuit fault occurs in the DC power distribution system by judging whether the rate of change of the current of the first power device is greater than the set current rate of change is faster than the method of judging whether a short - circuit fault occurs in the DC power distribution system by judging whether the current detected by the Hall detector is greater than the set current value, and can judge whether a short - circuit fault occurs in the DC power distribution system more timely.

[0036] The control module is also used to send Figure 2 the DO pulses in to control the closing and opening of the circuit breakers QF1 and QF2.

[0037] Among them, Figure 2 the DI signal in is the feedback of the closing and opening state of the circuit breaker, enabling the FPGA chip to obtain the closing and opening state of the circuit breaker according to the obtained DI signal.

[0038] It should be understood that the above - mentioned specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention.

Claims

1. A blocking device for a DC power distribution system, characterized in that: It comprises a control module and a blocking module; the blocking module comprises a two-quadrant DC / DC converter, wherein two ends of a branch having a first power device and a second power device connected in series in the converter are used to connect to the power supply end of a DC power distribution system, and two ends of the second power device are used to connect to the load end of the DC power distribution system; the control module is used to judge whether a short-circuit fault occurs in the DC power distribution system, and in the case of a short-circuit fault, if the current of the DC power distribution system is greater than a blocking current setting, the first power device is controlled to be turned off, otherwise, a current closed-loop control is performed according to the difference between the current of the DC power distribution system and the blocking current setting, so as to control the opening and closing of the first power device according to the control amount output by the current closed-loop control; the blocking current setting is less than the maximum withstand current of the load end of the DC power distribution system, and the current of the DC power distribution system under the current closed-loop control meets the triggering condition of the differential protection.

2. The blocking device of the DC power distribution system according to claim 1, characterized in that: The control module is also used to perform voltage closed-loop control according to the difference between the real-time voltages at the power supply end and the load end of the DC power distribution system when it is determined that the DC power distribution system has no short-circuit fault, so as to control the opening and closing of the first power device according to the control amount output by the voltage closed-loop control.

3. The blocking device of the DC power distribution system according to claim 1 or 2, characterized in that: The blocking module also includes an RCD buffer circuit connected in parallel at both ends of the first power device in the two-quadrant DC / DC converter.

4. The blocking device of the DC power distribution system according to claim 1 or 2, characterized in that: The blocking module also includes capacitors connected in parallel at both ends of a branch in which a first power device and a second power device in the two-quadrant DC / DC converter are connected in series.

5. The blocking device of the DC power distribution system according to claim 1 or 2, characterized in that: The blocking module further includes an inductor connected in series to a line for connecting two ends of the second power device and a load end of the DC power distribution system.

6. The blocking device of the DC power distribution system according to claim 5, characterized in that: A Hall detector is also arranged in series on the line where the inductor is located, and the Hall detector is used to detect the current on the line; the method for determining whether the DC power distribution system has a short circuit fault includes: determining whether the current detected by the Hall detector is greater than the set current value, and if so, determining that a short circuit fault has occurred in the DC power distribution system.

7. The blocking device of the DC power distribution system according to claim 5, characterized in that: The method for determining whether a short circuit fault occurs in a DC power distribution system includes: determining a rate of change of a current flowing through a first power device in a two-quadrant DC / DC converter based on a voltage change and an inductance of the first power device within a set time; if the rate of change of the current flowing through the first power device in the two-quadrant DC / DC converter is greater than a set current change rate, determining that a short circuit fault occurs in the DC power distribution system.

8. The blocking device of a DC power distribution system according to claim 1 or 2, characterized in that: The lower limit threshold of the blocking current constant is in the range of 1.2 to 10 times the rated current of the load at the load end of the DC power distribution system, so that the current of the DC power distribution system under current closed-loop control meets the triggering condition of differential protection.

9. The blocking device of a DC power distribution system according to claim 1 or 2, characterized in that: The blocking module in the blocking device of the DC distribution system also includes a first circuit breaker and a second circuit breaker; the two ends of the branch in which the first power device and the second power device are connected in series in the two-quadrant DC / DC converter in the blocking module of the blocking device of the DC distribution system are connected to the power supply end of the DC distribution system through the first circuit breaker, and the two ends of the second power device are connected to the load end of the DC distribution system through the second circuit breaker.

Images