CN109659911A

CN109659911A - A kind of failure self-cleaning MMC topology suitable for multiterminal element and DC grid

Info

Publication number: CN109659911A
Application number: CN201811523957.9A
Authority: CN
Inventors: 贾秀芳; 李嘉龙; 俞永杰; 李帅; 赵成勇; 许建中
Original assignee: North China Electric Power University
Current assignee: North China Electric Power University
Priority date: 2018-12-13
Filing date: 2018-12-13
Publication date: 2019-04-19

Abstract

The invention relates to a fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grids, belonging to the technical field of multi-terminal direct current and direct current power grids; the fault self-clearing MMC topology comprises a converter unit and a line unit, wherein the converter unit is improved by The structure of the converter station is composed; the line unit includes a fast mechanical switch, a group of parallel capacitors and a number of series diodes. When the fault self-clearing MMC topology is in normal operation, its converter unit operates as a converter station, which is the same as the normal working state; since the line unit is not connected to the line, it does not affect the normal operation of the system; Coordinate control of converter unit and line unit to achieve fault removal and isolation.

Description

A kind of failure self-cleaning MMC topology suitable for multiterminal element and DC grid

Technical field

The present invention relates to a kind of failure self-cleaning MMC topologys suitable for multiterminal element and DC grid, and it is straight to belong to multiterminal Stream, DC grid field.

Background technique

Flexible DC transmission has obtained more and more attention, multi-terminal HVDC transmission and DC grid due to plurality of advantages Become following trend.But since the fault current of DC line fault does not have zero crossing, so cannot be as ac transmission Utilize zero crossing arc extinguishing like that, this brings very big difficulty to the realization of dc circuit breaker, current implementation method be divided into Under it is several: current zero-crossing point is generated based on superimposed oscillation electric current, and then realizes electric current disjunction, the disadvantage is that turn-off delay is too long, is closed Power-off stream is limited；DC line increases inversion-rectification link, and the exchange side after inversion cuts off electric current with AC circuit breaker, lacks Point is off delay greatly, could turn off until current zero-crossing point, and loss is big, involves great expense；With a large amount of power electronics device Part series connection, above lightning arrester connected in parallel, electric current flows through the lower branch of impedance in normal work, play the role of drop it is low-loss, Electric current is first transferred to power electronics branch when off, then opens disconnecting switch, then is closed with power electronic devices It is disconnected, fault energy is absorbed with arrester.The disadvantage is that cut-off current is limited, and electric current is first transferred to power electronics when shutdown Branch also waits for disconnecting switch and fully opens, increases turn-off delay to a certain extent.Part is independent of direct current interruption The fault clearance strategy of device, such as half full mixed topology are difficult to realize preferable due to biggish number of devices and running wastage Economy.The exploitation of dc circuit breaker in the following multiterminal element and DC grid still has many problems demands to solve, research Suitable for high voltage, high current occasion, and with good rapidity, economy DC Line Fault remove strategy have become it is urgent It is essential and wants.

Summary of the invention

In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a kind of suitable for multiterminal element and DC grid Failure self-cleaning MMC topology.

It is an object of the invention to overcome current high voltage DC breaker voltage class lower, shutdown is slower, and cost is excessively high The shortcomings that.

The technical scheme adopted by the invention is that: when operating normally, inverter unit is run as converter station, with Converter station function is identical, and line unit does not influence the normal operation of system；When DC line fault occurs, inverter unit is logical The IGBT triggering for making to be connected in parallel between bridge arm reactance is crossed, the DC potential of inverter is down to close to zero potential；At this time on route Capacitor current potential be higher than inverter, discharge to inverter side so that the fault current between capacitor and inverter reduces, work as failure When current reduction is to zero, the disconnecting switch on route can disjunction faulty line；The energy of the route storage of the capacitor other side can To consume energy by diode continuousing flow circuit.

Compared with prior art, the present invention has the advantage that are as follows:

1, turn-off delay is small, since mechanical switch speed is slower, at least needs 2ms, the electricity in conventional hybrid formula breaker Power electronics cut-off circuit is connected in parallel on mechanical switch branch road, and needing to fully open to mechanical switch could the cutout of latch power electronics Circuit, then there are also the endergonic process in energy absorption circuit；And the Fast mechanical switch of the breaker does not have parallel branch, in event When barrier, execute after backup shutdoun and electric current transfer operation can disjunction Fast mechanical switch, after Fast mechanical switch is opened Failure is just removed, and turn-off delay is reduced.

2, at low cost, the converter station of current engineer application, which is added some circuits, can be transformed into inverter unit, normally Its function as converter station is not influenced when operation；It connects no longer as hybrid circuit breaker on every route and largely controls entirely Type device, saves cost.

3, economical operation, a large amount of concatenated wholly-controled devices and energy absorption circuit due to hybrid circuit breaker configuration Idle state is in when route operates normally, and the program only has energy absorption circuit when operating normally in idle shape State, running wastage greatly reduce；Inverter unit can be used as converter station use when normal, improve utilization rate.

Detailed description of the invention

The following further describes the present invention with reference to the drawings.

Fig. 1 shows a kind of failure self-cleaning MMC topological structure schematic diagram suitable for multiterminal element and DC grid, packet Include inverter unit and breaking units, wherein line unit is made of Fast mechanical switch, capacitor, diode；

Fig. 2 shows inverter unit structural schematic diagram, between the upper and lower bridge arm inductance of traditional converter station it is in parallel by Branch made of IGBT switching group and Diode series, while metal oxide arrester in parallel；

Fig. 3 shows the schematic illustration of fault clearance process；

Fig. 4 shows fault clearance operational flowchart；

Fig. 5 shows reclosing strategic process schematic diagram.

Specific embodiment

Below in conjunction with the attached drawing in the embodiment of the present application, technical solutions in the embodiments of the present application carries out clear, complete Site preparation description.

It is a kind of suitable for the failure self-cleaning MMC topological structure of multiterminal element and DC grid as shown in Figure 1, include the change of current Device unit and breaking units, wherein line unit is made of Fast mechanical switch, capacitor, diode；Fig. 2 is to inverter topology Structure has carried out further displaying, in parallel by IGBT switching group and diode between the upper and lower bridge arm inductance of traditional converter station The branch being connected in series, while metal oxide arrester in parallel；Wherein, the quantity of IGBT switching group and concatenated diode It is determined by bridge arm reactance both end voltage, usually up to a hundred.

Fault clearance principle by being latched all submodules, while triggering the T in ICM as shown in figure 3, when failure₃, will Inverter current potential is down to close to zero potential, at this point, other are simultaneously to fault point and the inverter feed-in fault current；Capacitance voltage For AC line voltage, capacitor discharges to both ends at this time, wherein the part discharged to converter station just will be by disconnecting switch Current canceling, so that disconnecting switch can disconnect faulty line.

Fault clearance operational flowchart is as shown in Figure 4:

t₀Direct-current short circuit failure occurs for the moment, and after wave transmission delay, fault current starts to increase rapidly all converter stations Greatly.Due to the presence of line inductance, the large percentage of fault current shared by the closer inverter of distance fault point.

t₁The DC voltage of proximal end inverter is reduced to the on-state voltage drop of IGBT as failure is positioned by the moment, so that The energy stored in DC line is dissipated by the circuit that diode, faulty line and fault point are formed, and not will cause electricity Stream was decayed slow problem.

t₂At the moment, when the current attenuation in disconnecting switch is to 0, disjunction UFD is with isolated fault route.

t₃At the moment, as UFD fracture reaches maximum breaking gap, failure is successfully isolated, and at this time can restore inverter To normal operating condition.

Reclosing operation process is as shown in figure 5, first determine whether fault type, for permanent fault, without reclosing, Directly carry out trouble hunting；When transient fault, have the UFD with point combined floodgate ability for sulfur hexafluoride gas type UFD etc., it can be with Directly it is closed；For not having the UFD of electrification combined floodgate ability, then needs first to carry out Converter DC-side drop voltage operation, be UFD Combined floodgate create conditions, to restore inverter normal operating condition after UFD closing success again.

Finally it should be noted that: described embodiment is only some embodiments of the present application, rather than whole realities Apply example.Based on the embodiment in the application, those of ordinary skill in the art are obtained without making creative work Every other embodiment, shall fall in the protection scope of this application.

Claims

1. A fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grid, is characterized in that: comprise converter unit (1), line unit (2); Wherein converter unit comprises full control type device (IGBT, IGCT, etc.), diodes, bridge arm inductors, metal oxide arresters, wires, etc.; line units include fast mechanical switches, capacitors, diodes, etc.

2. a kind of fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grid according to claim 1 is characterized in that: the composition structure of its converter unit is: between the upper and lower bridge arm inductances of the traditional converter station A branch circuit consisting of several IGBT switch groups and diodes in series is connected in parallel, and metal oxide arresters are connected in parallel; the converter station adopts topology such as half-bridge MMC, full-bridge MMC, and half-full-bridge hybrid MMC, and the circuit is turned off during normal operation. , the converter unit operates as a converter station, and has the same function as the converter station, and is used as a converter unit to assist in clearing the fault when a fault occurs.

3. A kind of fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grid according to claim 1, it is characterized in that: line unit is made up of fast mechanical switch, capacitor, diode, wherein fast mechanical switch is connected in series on the line, and capacitor. It is connected in parallel with the diode to form a residual current discharge circuit, which is connected between the line and the ground electrode.

4. a kind of fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grid according to claim 1 is characterized in that: when direct current line fault occurs, the converter unit is connected in parallel between the bridge arm reactance by The IGBT is triggered to reduce the DC potential of the converter to near zero potential; at this time, the potential of the capacitor on the line is higher than that of the converter, and the discharge to the converter side reduces the fault current between the capacitor and the converter. When the current is reduced to zero, the isolating switch on the line can disconnect the faulty line; the energy stored in the line on the other side of the capacitor can be dissipated through the diode freewheeling loop.

5. a kind of fault self-clearing MMC topology suitable for multi-terminal direct current and direct current power grid according to claim 1, is characterized in that: after the line fault is cleared, by detecting whether oscillation occurs in the reduction process of the current on the cut off line, The type of fault can be judged, and then the reclosing strategy can be determined; if the current oscillates, the fault is an instantaneous fault, and the reclosing operation can be performed; if the current does not oscillate, the fault is a permanent fault, and reclosing cannot be performed at this time; The method can avoid the system coincident with the permanent failure and lead to greater losses.