CN112968433A

CN112968433A - Capacitor clamping type direct current breaker topology with self-adaptive reclosing capacity and suitable for direct current power grid

Info

Publication number: CN112968433A
Application number: CN202110334298.XA
Authority: CN
Inventors: 蒋纯冰; 赵成勇
Original assignee: North China Electric Power University
Current assignee: North China Electric Power University
Priority date: 2021-03-29
Filing date: 2021-03-29
Publication date: 2021-06-15

Abstract

The invention relates to a capacitor clamping type DC circuit breaker topology with adaptive reclosing capability suitable for a DC power grid, belonging to the technical field of multi-terminal DC and DC power grids; the DC circuit breaker topology comprises a current flow module, a capacitor clamping module and a The self-adaptive reclosing judgment module, in which the flow-through module is composed of a fast mechanical switch, a thyristor, and a DC reactor, and the capacitor clamping module is composed of a fast mechanical switch, a thyristor, a capacitor, and a fast mechanical switch; composition. The DC circuit breaker topology actively boosts the voltage through the capacitor clamp module, so that the potential voltage at point w and the DC side system voltage form a voltage difference, so that the DC fault line is quickly isolated, and at the same time, it ensures that the converter is not damaged during the whole process of fault ride-through. No blocking occurs; the self-adaptive reclosing judgment module can distinguish between transient faults and permanent faults, avoiding blind reclosing and permanent faults causing serious damage to the system.

Description

Capacitor clamping type direct current breaker topology with self-adaptive reclosing capacity and suitable for direct current power grid

Technical Field

The invention relates to a capacitance clamping type direct current breaker topology with self-adaptive reclosing capability and suitable for a direct current power grid, and belongs to the field of multi-terminal direct current and direct current power grids.

Background

The flexible direct-current power grid technology based on the modular multilevel converter has the advantages of active and reactive decoupling control, no commutation failure, low harmonic content and the like, can realize multi-power supply and multi-drop point power receiving, and is an important means for interconnection of power grids and large-scale renewable energy grid connection in the future. In large-capacity and long-distance power transmission projects, overhead lines are the main transmission mode, but the overhead lines are exposed to the outside air for a long time, so that high fault risks exist. When a short-circuit fault occurs in a direct-current power grid, fault current develops rapidly, and a direct-current system does not have a natural zero crossing point, so that higher requirements are provided for a direct-current fault isolation strategy. At present, the most common fault isolation strategy is to adopt a direct current circuit breaker, and a hybrid direct current circuit breaker has the advantages of low-dynamic loss characteristic and quick breaking dual characteristics, and is the currently preferred direct current circuit breaker type. However, the hybrid dc circuit breaker requires a large number of IGBT devices connected in series and parallel, which makes the hybrid dc circuit breaker expensive. The method is partially independent of a fault clearing strategy of the direct current breaker, such as a semi-full hybrid topology and the like, and the investment cost and the operation cost are higher due to more device usage, so that the economy is reduced to a certain extent. In addition, the above topologies cannot realize adaptive reclosing, i.e., cannot determine whether the fault type is a transient fault or a permanent fault. If the blind reclosing is in a permanent fault, the system can not be recovered to normal power supply, and the damage to the system stability and the damage to electrical equipment are far more than the damage to the system when the fault occurs in a normal operation state.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a capacitance clamping type direct current breaker topology which is suitable for a direct current power grid and has self-adaptive reclosing capability.

The invention aims to overcome the defects that the current high-voltage direct-current circuit breaker is high in price and cannot realize self-adaptive reclosing.

The technical scheme adopted by the invention is as follows: when the system normally operates, the thyristor in the through-current module is in a conducting state, and current flows through the through-current module with lower impedance; fast mechanical switch UFD in capacitive clamping module when DC line fault occurs₂、UFD₄And opening and closing the fast mechanical switches UFD3 and UFD 5. Through time delay, quick mechanical switch UFD₂、UFD₃、UFD₄And UFD₅After the action is finished, the thyristor V is triggered simultaneously₃. Clamping capacitor C_p1、C_p2The parallel connection is changed into the series connection, the equivalent capacitor voltage is changed into 2 times of the clamp capacitor pre-charging voltage, the direct current fault current is forced to be reduced to zero, and therefore the thyristor V₁Self-turn-off, fast mechanical switch UFD₁Providing zero current open-brake condition, UFD₁And after the brake is opened, the fault line is successfully isolated. Clamping capacitor C_p1、C_p2And an inductor C_p1、C_p2Form an LC resonant circuit, C_p1、C_p2Energy of C_p1、C_p2Absorption up to the clamp capacitance C_p1、C_p2End of discharge, at which time reverse charging is started, L_w、L_dcWill be transferred back to C_p1、C_p2However, from the capacitance charging characteristic, when L is_w、L_dcEnergy transfer back to C_p1、C_p2Then, C_p1、C_p2Will change in polarity, when the clamp capacitor C is present_p1、C_p2The voltage is opposite in polarity to the initial precharge state, completing the energy transfer. After the energy transfer process is finished, starting adaptive reclosing and closing the UFD₂、UFD₄And UFD₆And simultaneously opening UFD₃、UFD₅After time delay, UFD₂、UFD₃、UFD₄、UFD₅And UFD₆And finishing the action. When the fault type is permanent fault, the self-adaptive reclosing judgment module is a clamping capacitor C_p1、C_p2Providing a discharging path, wherein the current of the self-adaptive reclosing judging module is not zero at the moment; when the fault type is transient fault, the adaptive reclosing judgment module cannot be the clamping capacitor C at the moment because the fault point is eliminated_p1、C_p2And providing a discharging path, wherein the current of the self-adaptive reclosing judging module is nearly zero. Therefore, whether the current of the module is zero or not can be judged according to the self-adaptive reclosing, and the fault type is judged. Compared with the prior art, the invention has the advantages that:

1. the hybrid direct current breaker is good in economy, and because IGBT devices in the power electronic cut-off branch circuit in the hybrid direct current breaker need to be designed according to the requirements of bearing higher direct current voltage and larger fault current, the quantity of IGBTs in the power electronic cut-off branch circuit is large; according to the invention, the capacitor clamping module is used for actively boosting, so that a direct-current fault circuit is quickly isolated, and the situation that a converter is locked in the whole fault ride-through process is ensured; the invention replaces the high-price full-control device IGBT with the thyristor with good economic performance and strong voltage and current resistance, thereby reducing the investment cost.

2. The current value of the self-adaptive reclosing judging module is analyzed, so that the self-adaptive reclosing is realized.

Drawings

The invention is further described below with reference to the accompanying drawings.

Fig. 1 shows a capacitance clamping type dc circuit breaker topology with adaptive reclosing capability suitable for a dc power grid, belonging to the technical field of multi-terminal dc and dc power grids; the direct current breaker topology comprises a through-current module, a capacitance clamping module and a self-adaptive reclosing judgment module;

FIG. 2 shows the current paths during a fault detection phase;

FIG. 3 shows the current paths during a fault line isolation phase;

FIG. 4 illustrates the current flow path during the energy transfer phase;

fig. 5 shows the through-current path during the adaptive reclosing phase.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

A capacitor clamping type direct current breaker topology with self-adaptive reclosing capability suitable for a direct current power grid is shown in figure 1 and comprises a through-current module, a capacitor clamping module and a self-adaptive reclosing judgment module; the current flowing module consists of a quick mechanical switch, a thyristor and a direct current reactor, and the capacitance clamping module consists of a quick mechanical switch, a thyristor and a capacitor; the self-adaptive reclosing judging module consists of a quick mechanical switch and a resistor.

Through-flow path at fault detection stagePaths are shown in FIG. 2, assuming t₀At the moment, a single-pole earth fault occurs on the line, and due to the fault detection delay, the fault current still flows through the through-current module.

The current path during the fault line isolation phase is shown in FIG. 3, with the fault detected and localized, at t₁Momentarily clamping UFD in a module₂、UFD₄Switching off and simultaneously closing UFD₃、UFD₅. UFD with time delay of delta₂、UFD₃、UFD₄And UFD₅After the action is finished, triggering V simultaneously₃I.e. t₂At time, the clamp capacitor C_p1、C_p2The parallel connection is changed into the series connection, the equivalent capacitor voltage is changed into 2 times of the clamp capacitor pre-charging voltage, the direct current fault current is forced to be reduced, and the direct current fault current is at t₃Time zero crossing, at this time V₁Self-turn-off as UFD₁Providing zero current brake-separating condition, and delaying by delta t, UFD₁And after the brake is opened, the fault line is successfully isolated.

The flow path during the energy transfer phase is shown in FIG. 4 at t₃At time, the clamp capacitor C_p1、C_p2And an inductance L_w、L_dcForm an LC resonant circuit, C_p1、C_p2Is given by energy L_w、L_dcAnd (4) absorbing. At t₄At time, the clamp capacitor C_p1And C_p2End of discharge, at which time reverse charging is started, L_w、L_dcWill be transferred back to C_p1、C_p2However, from the capacitance charging characteristic, when L is_w、L_dcEnergy transfer back to C_p1、C_p2Then, C_p1、C_p2Will change polarity. At t₅At the moment, the current of the resonant loop crosses zero and is a thyristor valve group V₃Providing a natural turn-off condition when the clamp capacitor C is present_p1、C_p2The voltage is of opposite polarity to the initial precharge state.

The through-current path at the adaptive reclosing judgment stage is shown in FIG. 5 at t₆At the moment, the judgment of reclosing is started, and the UFD is closed₂、UFD₄And UFD₆And simultaneously opening UFD₃、UFD₅After a delay of Δ t, UFD₂、UFD₃、UFD₄、UFD₅And UFD₆After the movement is finished, i.e. t₇At time, the clamp capacitor C_p1、C_p2The discharge is started. In order to reduce the risk of error judgment of reclosing, a current judgment threshold value is set, and I can be used_vaSet to 1 kA. When the fault type is permanent fault, the self-adaptive reclosing judgment module is C_p1、C_p2The provided discharge path, the current I of the self-adaptive reclosing judging module at the moment_reGreater than a discrimination threshold I_va(ii) a When the fault type is transient fault, the self-adaptive reclosing judgment module cannot be C_p1、C_p2Providing a discharge path, and judging the module current I by the adaptive reclosing_reLess than a discrimination threshold I_va. Therefore, the current I of the module can be judged according to the self-adaptive reclosing_reWhether or not it is greater than the discrimination threshold I_vaThus realizing the self-adaptive reclosing.

Finally, it should be noted that: the described embodiments are only some embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Claims

1. a capacitor clamp type DC circuit breaker topology with adaptive reclosing capability suitable for DC power grid, it is characterized in that: comprising a current flow module, a capacitor clamp module and an adaptive reclosing judgment module; wherein the current flow module It is composed of fast mechanical switch, thyristor, and DC reactor. The capacitor clamping module is composed of fast mechanical switch, thyristor, and capacitor. The adaptive reclosing judgment module is composed of fast mechanical switch and resistor.

2. A capacitor-clamped DC circuit breaker topology with adaptive reclosing capability suitable for DC power grid according to claim 1, characterized in that: the current flow module is composed of a fast mechanical switch, a thyristor, and a DC reactor , in which the bidirectional parallel thyristor is connected in series with the fast mechanical switch and the DC reactor.

3. A capacitor clamping type DC circuit breaker topology with adaptive reclosing capability suitable for DC power grid according to claim 1, characterized in that: the capacitor clamping module is composed of a clamping capacitor, an ultra-fast mechanical switch, a The anti-parallel thyristor valve group and the buffer inductor are formed; the capacitor clamping module can isolate the faulty line by raising the DC line voltage and forcing the line current to drop to zero.

4. A capacitor-clamped DC circuit breaker topology with self-adaptive reclosing capability suitable for a DC power grid according to claim 1, wherein the self-adaptive reclosing judgment module is composed of a discriminating resistor and a discriminating switch; When the fault is a transient fault, the power grid can be restored to normal operation through the reclosing operation, and determining whether it is a transient fault is the premise of the reclosing operation, and the instantaneous fault can be distinguished by the current value of the adaptive reclosing judgment module with permanent failure.