A medium voltage DC power grid feed-out protection device

Abstract

The invention discloses a medium-voltage DC power grid feed protection device, comprising a power electronic switch assembly arranged on a DC positive line and / or a DC negative line, the power electronic switch assembly being used to protect the line and load of the DC outflow collecting bus, one end of the power electronic switch assembly being connected to a current limiting reactor, the current limiting reactor being connected to a line-side load, and the other end of the power electronic switch assembly being connected to the DC collecting bus through a main contactor and a main isolating switch in sequence; when circuit breaking or abnormality is required, the power electronic switch assembly disconnects the line before the main contactor, and disconnects the main contactor after the line current drops to near zero; when the line is connected, the power electronic switch is first triggered to conduct, and then the main contactor is closed; the invention can quickly block a short circuit caused by a line short circuit for a branch of a DC power grid where power flows out in one direction.

Description

Technical Field

[0001] The invention relates to the technical field of circuit protection devices, and in particular to a medium-voltage direct current grid feed-out protection device. Background Art

[0002] Medium-voltage DC grids often use protection devices with mechanical contacts. When a short circuit occurs, the voltage will drop to less than 10% for more than 2ms. For many sensitive microgrid equipment, the 2ms ultra-low voltage process may cause fault downtime and production losses. For off-grid microgrids, the 2ms ultra-low voltage process may cause the grid to collapse.

[0003] The prior art has power electronic DC circuit breakers, but these circuit breakers are bidirectional breaking circuit breakers, and a large number of diode components are provided to provide bidirectional breaking capacity, resulting in large losses and high costs. Moreover, these DC circuit breakers do not have active short-circuit current limiting devices inside, and the speed of change of the short-circuit current is limited by the parameters of the external power grid, which has great uncertainty. In situations where the short-circuit impedance of the external power grid itself is small, such as a power grid with a capacitor support device, these DC circuit breakers must also be used in conjunction with a dedicated current limiting device, so they are large in size and high in cost. Summary of the invention

[0004] The object of the present invention is to provide a medium voltage DC grid feed protection device to solve the technical problems of large size, high cost and short circuit delay in the prior art when used with a dedicated current limiting device.

[0005] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0006] A medium-voltage DC power grid feed-out protection device comprises a power electronic switch assembly arranged on a DC positive line and / or a DC negative line, one end of the power electronic switch assembly is connected to a current limiting reactor, the current limiting reactor is connected to a line-side load, the other end of the power electronic switch assembly is connected to a DC collection busbar through a main contactor and a main isolating switch in sequence, and the power electronic switch assembly can perform unidirectional protection on a current from the DC positive line to the DC negative line;

[0007] Wherein, when a circuit break is required or an abnormality occurs, the power electronic switch assembly disconnects the circuit before the main contactor, and disconnects the main contactor after the circuit current drops to near zero;

[0008] When the line is connected, the power electronic switch is triggered to conduct first, and then the main contactor is closed.

[0009] As a preferred solution of the present invention, at least two power electronic switch components are arranged in series and are arbitrarily distributed on the DC positive line and / or the DC negative line.

[0010] As a preferred embodiment of the present invention, at least two adjacent power electronic switch components are combined into a power electronic switch unit, wherein a component control device and a heat sink are provided in each power electronic switch unit, and the power electronic switch components in the same power electronic switch unit share one component control device.

[0011] As a preferred solution of the present invention, it also includes a current detection device arranged on the DC positive line and / or the DC negative line, and a system control device connected to the current detection device;

[0012] The current detection device is used to detect the line current and transmit the current signal to the system control device;

[0013] The system control device is communicatively connected to the component control device of the power electronic switch unit. The system control device is used to send an instruction to the component control device to disconnect all power electronic switch units after determining that the current signal exceeds a preset threshold, so as to disconnect all power electronic switch components.

[0014] As a preferred solution of the present invention, each of the power electronic switch components is connected to a voltage detection device, and the voltage detection device is connected to the system control device. The voltage detection device is used to detect the voltage across the power electronic switch component and transmit the voltage signal to the system control device. The system control device is used to send an instruction to the component control device to disconnect all power electronic switch units when it is determined that any of the voltage signals exceeds a preset threshold, so as to disconnect all power electronic switch components.

[0015] As a preferred solution of the present invention, each of the power electronic switch components includes a power electronic switch, a static voltage balancing circuit, a dynamic overvoltage absorption circuit, a line energy absorption circuit and a reverse conducting diode arranged in parallel;

[0016] Two ends of the power electronic switch are connected to circuits.

[0017] As a preferred solution of the present invention, the dynamic overvoltage absorption circuit is a resistor in series with a capacitor;

[0018] The static voltage balancing circuit is a voltage balancing resistor;

[0019] The line energy absorption circuit is a metal oxide varistor;

[0020] The power electronic switch is IGBT, IGCT or IEGT.

[0021] As a preferred solution of the present invention, the installation direction of the positive and negative electrodes of the diode is opposite to the DC conducting direction from the DC positive electrode line to the DC negative electrode line.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention can quickly block the short circuit caused by line short circuit for the branch of the DC power grid where power flows out in one direction, has low conduction loss and high working efficiency, and suppresses the current rising speed during short circuit by setting a current limiting reactor, so that within a certain time after the short circuit occurs, the short circuit current is lower than the cut-off current of the DC circuit breaker, and the circuit breaker can perform reliable disconnection protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0025] Figure 1 A structural block diagram of a feed-out protection device provided in an embodiment of the present invention;

[0026] Figure 2 A structural block diagram of a power electronic switch assembly provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 and Figure 2 As shown, the present invention provides a medium voltage DC power grid feed-out protection device, which specifically includes the following embodiments. Embodiment 1:

[0029] The DC grid feed protection device comprises a power electronic switch assembly arranged on a DC positive line or a DC negative line, one end of the power electronic switch assembly is connected to a current limiting reactor, the current limiting reactor is connected to a line-side load, and the other end of the power electronic switch assembly is connected to a DC collection busbar through a main contactor and a main isolating switch in sequence, and the power electronic switch assembly is used to protect the line and load of the DC outflow collection busbar.

[0030] Among them, when circuit breaking or abnormality is required, the power electronic switch component disconnects the line before the main contactor, and disconnects the main contactor after the line current drops to near zero.

[0031] When the line is connected, the power electronic switch is triggered to conduct first, and then the main contactor is closed.

[0032] Specifically, the current-limiting reactor can limit the rate of increase of the short-circuit current, and the power electronic switch assembly used in this device can perform a fast disconnection operation in less than 0.02ms. Therefore, no matter how small the short-circuit impedance of the external power grid is, the current-limiting reactor built into this device can ensure that within 0.02ms, the short-circuit current does not exceed the DC current breaking capacity of the power electronic switch of this device. In contrast, hybrid DC circuit breakers, or mechanical DC circuit breakers, have a breaking time of more than 2ms, and the short-circuit current increase rate of power electronic DC circuit breakers without current-limiting reactors may produce a short-circuit current that exceeds its breaking capacity.

[0033] In this embodiment, a current limiting reactor is arranged in the feed protection device, which can suppress the current rising speed during short circuit, so that within a certain time after the short circuit occurs, the short circuit current is lower than the cut-off current of the feed protection device, and the feed protection device can perform reliable disconnection protection.

[0034] In addition, the use of a unidirectional protection structure reduces the static loss of the rectifier diode, reduces the loss of the feed-in protection device for feed-out applications (energy flows from the DC grid to the line-side load), and improves the efficiency of the feed-in protection device.

[0035] The purpose of the main isolating switch is for maintenance isolation, and the main contactor is set to allow the main contactor to bear the system voltage as soon as possible when the power electronic switch component is in the disconnected state, avoiding the power electronic switch component from bearing the system voltage for a long time, thereby improving the reliability of the system.

[0036] Among them, at least two power electronic switch components are arranged in series and are arbitrarily distributed on the DC positive line or the DC negative line.

[0037] The voltage of a single power electronic switch component is relatively low, typically with an operating voltage of 2 kV and a maximum withstand voltage of 4.5 kV. The operating voltage of a typical medium-voltage DC circuit breaker is 20 kV, so multiple power electronic switch components are required to be connected in series to form a medium-voltage DC circuit breaker.

[0038] At least two adjacent power electronic switch components are combined into a power electronic switch unit, wherein a component control device is arranged in each power electronic switch unit, and the power electronic switch components in the same power electronic switch unit share a component control device.

[0039] In this embodiment, the same power electronic switch unit shares a heat sink, and the combined power electronic switch unit has a small size and low cost, and makes reasonable use of the heat dissipation and withstand voltage capabilities of the device and the conductive electrode withstand voltage capabilities.

[0040] A temperature sensor is installed on the radiator, and the temperature is sampled through the component control device and sent to the system control device through optical fiber. A speed-adjustable fan is used for air cooling. According to the measured radiator temperature, the fan speed is adjusted so that the system can operate at a reasonable radiator temperature and a low fan power consumption point.

[0041] In addition, a current detection device is provided on the DC positive line or the DC negative line, and a system control device connected to the current detection device.

[0042] The component control device is a control chip system that communicates with the system control device. The system control device sends commands to the power electronic switch and detects the operating status of the power electronic switch.

[0043] The system control device and the component control device are connected by optical fiber. The system control device sends closing and disconnecting instructions to the component control device through optical fiber, and the component control device reports its own status to the system control device through optical fiber.

[0044] The current detection device is used to detect the line current and transmit the current signal to the system control device; the system control device is communicatively connected with the component control device of the power electronic switch unit, and the system control device is used to send an instruction to the component control device to disconnect all power electronic switch units after determining that the current signal exceeds a preset threshold value, so as to disconnect all power electronic switch components.

[0045] Each power electronic switch component is connected to a voltage detection device, which is connected to the system control device. The voltage detection device is used to detect the voltage across the power electronic switch component and transmit the voltage signal to the system control device. The system control device is used to send an instruction to the component control device to disconnect all power electronic switch units when it determines that any voltage signal exceeds a preset threshold, so as to disconnect all power electronic switch components.

[0046] Furthermore, each power electronic switch assembly includes a power electronic switch, a static voltage balancing circuit, a dynamic overvoltage absorption circuit and a line energy absorption circuit arranged in parallel, and the two ends of the power electronic switch are connected to the line.

[0047] The dynamic overvoltage absorption circuit is a resistor in series with a capacitor; the static voltage equalization circuit is a voltage equalization resistor; the line energy absorption circuit is a metal oxide varistor;

[0048] The power electronic switch is an IGBT or an IGCT or an IEGT, and two ends of the power electronic switch are provided with reverse conducting diodes in parallel, and the positive and negative poles of the reverse conducting diodes are installed in the opposite direction to the DC conducting direction from the DC positive line to the DC negative line, so that the power electronic switch assembly can perform unidirectional protection on the current from the DC positive line to the DC negative line;

[0049] The dynamic overvoltage absorption circuit is used to make the voltages borne by each series-connected power electronic switch have better consistency during the turn-on and turn-off processes;

[0050] The static voltage balancing circuit is used to ensure that the voltages borne by the power electronic switches connected in series have good consistency in the continuous off state.

[0051] The line energy absorption circuit is used to limit the voltage generated by the current of the line inductance due to the shutdown of the power electronic switch within an acceptable range when the line inductance exists, and to limit the voltage across each power electronic switch within an acceptable range, and to consume the energy stored in the line inductance in the above process.

[0052] In specific applications, the feed protection device of this embodiment is installed on the line between the DC grid and the load, wherein the rated voltage of the DC grid is ±10kV, and the rated current of the feed protection is 200A-1200A; the power electronic switches on the DC positive line and the DC negative line use 6-10 IGBTs, IGCTs or IEGTs respectively, and each IGBT has a rated voltage of 3.3kV, 4.5kV or 6.5kV and a rated current of 0.65kA-3kA;

[0053] The dynamic overvoltage absorption circuit of IGBT adopts a resistor-capacitor series method, with a resistor value of 0.2Ω - 10Ω, a rated power of 100W, a capacitor value of 0.47uF - 20uF, and a rated voltage of 3.3kV-6.5kV;

[0054] The static voltage equalization circuit of IGBT uses a voltage equalization resistor with a resistance of 100kΩ – 3.3MΩ and a rated power of 50W – 500W.

[0055] The line energy absorption circuit uses a varistor, which is connected in parallel to each IGBT. The operating voltage is 1.8kV - 4.0kV, the residual voltage is 2.8kV - 5.9kV, the residual voltage current is 0.9kA - 5.5kA, and the energy is 5kJ - 100kJ.

[0056] The rated voltage of the main contactor is DC20kV, and the rated current is 250A – 1250A; the rated voltage of the main disconnector is DC20kV, and the rated current is 250A – 1250A.

[0057] For a branch of a DC power grid where power flows out in one direction, this implementation can quickly block a short circuit caused by a line short circuit, has low conduction loss and high working efficiency, and by setting a current limiting reactor, suppresses the current rise rate during a short circuit, so that within a certain time after the short circuit occurs, the short circuit current is lower than the cutoff current of this DC circuit breaker, and the circuit breaker can perform reliable disconnection protection. Embodiment 2:

[0058] Different from the first embodiment, the DC grid feed protection device comprises power electronic switch components arranged on the DC positive line and the DC negative line, and the power electronic switch components form a topologically symmetrical structure.

[0059] The advantage of setting a set of power electronic switch components in series on the DC positive line and the DC negative line in this embodiment is that when the switch is disconnected, both the positive and negative poles can provide a higher turn-off voltage. In contrast, if a switch is set on only one pole, when it is turned off, the other pole is still in a directly connected state, and at the same time, the communication and command time of the power electronic switch component based on the grid current control in this embodiment is generally less than 0.02ms.

[0060] Based on the above-mentioned DC grid feed-out protection device, this embodiment further provides a method for implementing grid protection, comprising the following steps:

[0061] (1) Closing, connecting and disconnecting the power electronic switch assembly first triggers the power electronic switch to respond, and then triggers the main contactor to respond.

[0062] Specifically, when the power electronic switch assembly is turned on, all power electronic switches are in the on state, and when the power electronic switch assembly is turned on, the power electronic switch is triggered to turn on first, and then the main contactor is closed.

[0063] When disconnecting the power electronic switch assembly, the power electronic switch is disconnected first, and after detecting that the current drops to less than a preset threshold, the main contactor is disconnected.

[0064] (2) Sampling the current of the DC grid, automatically disconnecting the power electronic switch and the main contactor in sequence according to the absolute value of the current, and providing overcurrent protection for the system. Specifically, the current is quickly sampled by the current detection device. When it is detected that the absolute value of the current exceeds the preset current protection value, the system control device sends an automatic disconnection instruction of the power electronic switch to the component control device, and disconnects the main contactor after the current drops to less than the preset threshold.

[0065] (3) Detect the voltage across each power electronic switch, automatically disconnect all power electronic switches and main contactors in sequence according to the absolute value of the voltage, and report fault information.

[0066] The voltage across each power electronic switch is detected in real time. When the voltage across a power electronic switch exceeds a preset threshold, the power electronic switch is deemed to be faulty. The system control device sends a signal to the component control device to automatically disconnect all power electronic switches and main contactors in a timed sequence, and the component control device reports the fault information to the system control device.

[0067] The above embodiments are only exemplary embodiments of the present application and are not intended to limit the present application. The protection scope of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and protection scope of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the protection scope of the present application.

Claims

1. A medium voltage DC power grid feed protection device, characterized in that: It comprises a power electronic switch assembly arranged on a DC positive line and / or a DC negative line, one end of the power electronic switch assembly is connected to a current limiting reactor, the current limiting reactor is connected to a line-side load, the other end of the power electronic switch assembly is connected to a DC collection busbar through a main contactor and a main isolating switch in sequence, and the power electronic switch assembly is used to protect the line and load of the DC flowing out of the collection busbar; Wherein, when a circuit break is required or an abnormality occurs, the power electronic switch assembly disconnects the circuit before the main contactor, and disconnects the main contactor after the circuit current drops to near zero; When the line is connected, the power electronic switch is first triggered to conduct, and then the main contactor is closed; At least two adjacent power electronic switch components are combined into one power electronic switch unit, wherein each power electronic switch unit is provided with a component control device and a heat sink, and the power electronic switch components in the same power electronic switch unit share one component control device and heat sink; Each of the power electronic switch components comprises a power electronic switch, a static voltage balancing circuit, a dynamic overvoltage absorption circuit, a line energy absorption circuit and a reverse conducting diode arranged in parallel, and the two ends of the power electronic switch are connected to the circuit; The dynamic overvoltage absorption circuit is a resistor in series with a capacitor; The static voltage balancing circuit is a voltage balancing resistor; The line energy absorption circuit is a metal oxide varistor; Each of the power electronic switch components is connected to a voltage detection device, which is connected to a system control device. The voltage detection device is used to detect the voltage across the power electronic switch component and transmit the voltage signal to the system control device. The system control device is used to send an instruction to the component control device to disconnect all power electronic switch units when it is determined that any of the voltage signals exceeds a preset threshold, so as to disconnect all power electronic switch components.

2. A medium voltage DC power grid feed protection device according to claim 1, characterized in that: The power electronic switch components are randomly distributed on the DC positive line and / or the DC negative line.

3. A medium voltage DC power grid feed protection device according to claim 1, characterized in that: The number of the power electronic switch components arranged on the DC positive line and the DC negative line is the same to form a topologically symmetrical structure.

4. A medium voltage DC power grid feed protection device according to claim 1, characterized in that: It also includes a current detection device arranged on the DC positive line and / or the DC negative line, and a system control device connected to the current detection device; The current detection device is used to detect the line current and transmit the current signal to the system control device; The system control device is communicatively connected to the component control device of the power electronic switch unit. The system control device is used to send an instruction to the component control device to disconnect all power electronic switch units after determining that the current signal exceeds a preset threshold, so as to disconnect all power electronic switch components.

5. A medium voltage DC power grid feed protection device according to claim 1, characterized in that: The power electronic switch is IGBT, IGCT or IEGT.

6. A medium voltage DC power grid feed protection device according to claim 1, characterized in that: The installation direction of the positive and negative electrodes of the diode is opposite to the DC conducting direction from the DC positive electrode line to the DC negative electrode line.

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