CN117200156A - Capacitive high-voltage direct-current circuit breaker with current limiting capability - Google Patents

Abstract

The invention discloses a capacitive high-voltage DC circuit breaker with current limiting capability, which includes: a DC power supply, a main current branch, a current limiting branch, a breaking branch, a bypass branch and an overhead line. The DC power supply and the main The input end of the current-flow branch is connected, and the output end of the main current-flow branch is connected to the overhead line; the DC power supply is connected to the input end of the current-limiting branch through the first diode, and the input end of the current-limiting branch passes through the second The diode is connected to the overhead line, the output end of the current limiting branch is connected to the input end of the breaking branch, the output end of the breaking branch is connected to the bypass branch, and the output end of the breaking branch also passes through a third diode , the eleventh thyristor is connected to the DC power supply, and the output end of the breaking branch is connected to the overhead line through the fourth diode. When the line is normal, the current of the DC power supply flows from the main through-flow branch into the overhead line; when a line fault occurs, the current-limiting branch commutates the fault current to the current-limiting branch, and separates the branch and the bypass branch. Road to discharge energy.

Description

A capacitor-type high-voltage DC circuit breaker with current-limiting capability

Technical field

The present invention belongs to the technical field of high-voltage DC circuit breakers, and specifically relates to a capacitor-type high-voltage DC circuit breaker with current limiting capability.

Background technique

In recent years, with the development and maturity of high-power power electronics technology, the scale of distributed energy generation has further expanded. The flexible DC grid based on modular multi-level converters has fast response speed, flexible operation mode, and is suitable for multi-terminal power supply. advantages have received widespread attention. Since most DC power grids use overhead lines for power transmission, the probability of failure is greatly increased, and the fault current will rise to dozens of times the rated current within a few milliseconds, posing severe challenges to the safety of power supply to the grid.

At present, after a short-circuit fault occurs in the high-voltage DC power grid, the DC circuit breakers at both ends of the line are tripped to isolate the fault. After the fault disappears, they are re-closed to restore the system to normal operation. The working method of the high-voltage DC circuit breaker (DCCB) can ensure the normal operation of non-fault areas to the maximum extent and effectively suppress the spread of fault current. High-voltage DC circuit breakers can generally be divided into three categories: mechanical, all-solid-state and hybrid. Among them, hybrid DC circuit breakers are composed of mechanical switches and power electronic devices. They take into account the advantages of mechanical and all-solid-state circuit breakers. They have significant advantages in terms of turn-off speed, service life and conduction loss. However, there are currently many other types of hybrid DC circuit breakers on the market. Most circuit breakers do not have fault current limiting capabilities and are relatively expensive.

Contents of the invention

In view of the problems existing in the prior art, the present invention provides a capacitive high-voltage DC circuit breaker with current limiting capability, which replaces the large-scale full control devices in the traditional DCCB with thyristors and diodes, while realizing the current interruption function. The cost is effectively reduced; at the same time, a current-limiting branch is added, and the charging and discharging characteristics of the capacitor are used to realize the switching of the current-limiting reactance and arrester, significantly reducing the fault current peak value.

In order to achieve the above technical objectives, the present invention adopts the following technical solution: a capacitive high-voltage DC circuit breaker with current limiting capability, including: DC power supply, main current branch, current limiting branch, breaking branch, and bypass branch. circuit and overhead lines, the DC power supply is connected to the input end of the main current branch, and the output end of the main current branch is connected to the overhead line; the DC power supply is also connected to the limiter through the first diode D ₁ The input end of the current branch is connected, the input end of the current limiting branch is also connected to the overhead line through the second diode _D2 , the output end of the current limiting branch is connected to the input end of the breaking branch, so The output end of the breaking branch is connected to the bypass branch, and the output end of the breaking branch is also connected to the DC power supply through the third diode D ₃ and the eleventh thyristor T _11. The output of the breaking branch The terminal is also connected to the overhead line through the fourth diode D ₄ ;

When the line is normal, the current of the DC power supply directly flows into the overhead line from the main current branch; when a line fault occurs, the current limiting branch of the present invention realizes the turn-off of the fifth thyristor T ₅ through the first commutation capacitor C ₁ , The fault current is commutated into the current-limiting branch, and energy is discharged through the breaking branch and the bypass branch.

Further, the main flow branch is composed of a first mechanical switch S ₁ and a load transfer switch LCS connected in series. One end of the first mechanical switch S ₁ is connected to the DC power supply, and the output end of the load transfer switch LCS is connected to an overhead power supply. Line connection.

Further, the load transfer switch LCS is composed of two insulated gate bipolar transistors IGBT and two diodes. The emitter of one insulated gate bipolar transistor IGBT is connected to the anode of one diode and the other insulated gate bipolar transistor respectively. The emitter of the transistor IGBT is connected, and the collector of one insulated gate bipolar transistor IGBT is connected to the cathode of a diode; the emitter of another insulated gate bipolar transistor IGBT is also connected to the anode of another diode, and the other insulated gate The collector of the bipolar transistor IGBT is connected to the cathode of another diode.

Further, the anode of the first diode D ₁ , the cathode of the third diode D ₃ , and the anode of the eleventh thyristor T ₁₁ are all connected to the DC power supply, and the cathode of the first diode D ₁ The anode of the third diode D ₃ and the cathode of the eleventh thyristor T ₁₁ are connected to the output end of the breaking branch; the anode of the second diode D ₂ is connected to the input end of the current limiting branch. The positive electrode and the negative electrode of the fourth diode D ₄ are both connected to the overhead line, the negative electrode of the second diode D ₂ is connected to the input end of the current limiting branch, and the positive electrode of the fourth diode D ₄ is connected to The output terminals of the disconnect branches are connected.

Further, the current-limiting branch includes: a first commutation capacitor C ₁ , a current-limiting resistor R _L , a current-limiting inductor _LL , a second mechanical switch S ₂ , a self-charging resistor R, a first thyristor T 1 , and a first thyristor T ₁ . The second thyristor T ₂ , the third thyristor T ₃ , the fourth thyristor T ₄ , the fifth thyristor T ₅ , the sixth thyristor T ₆ and the seventh thyristor T ₇ , the anode of the first thyristor T ₁ and the second thyristor T ₂ The anode and the cathode of the third thyristor T ₃ are connected as the input end of the current limiting branch; the cathode of the first thyristor T ₁ is connected to one end of the current limiting resistor _RL , and the other end of the current limiting resistor _RL They are respectively connected to the cathode of the fourth thyristor T ₄ and one end of the current limiting inductor _LL . The anode of the fourth thyristor T ₄ , the other end of the current limiting inductor _LL , the right plate of the first commutation capacitor C ₁ , The cathode of the sixth thyristor T ₆ and the anode of the seventh thyristor T ₇ are connected. The left plate of the first commutation capacitor C ₁ is connected to one end of the self-charging resistor R, the cathode of the second thyristor T ₂ and the third thyristor respectively. The anode of _T3 is connected to the anode of the fifth thyristor _T5 . The other end of the self-charging resistor R is connected to one end of the second mechanical switch _S2 . The other end of the second mechanical switch _S2 is grounded; The cathode of the fifth thyristor _T5 , the anode of the sixth thyristor _T6 , and the cathode of the seventh thyristor _T7 are connected to serve as the output end of the current limiting branch and connected to the input end of the breaking branch.

Further, the breaking branch includes: a second commutation capacitor C ₂ , a lightning arrester MOA, an eighth thyristor T ₈ , a ninth thyristor T ₉ and a tenth thyristor T ₁₀ . One end of the second commutation capacitor C ₂ , one end of the arrester MOA and the anode of the eighth thyristor T ₈ are connected as the input end of the breaking branch and connected to the output end of the current limiting branch; the other ends of the two commutation capacitors C ₂ are respectively connected to the ninth thyristor T The cathode of the ninth thyristor T ₁₀ is connected to the anode of the tenth thyristor T ₁₀ ; the anode of the ninth thyristor T ₉ , the cathode of the tenth thyristor T ₁₀ , the other end of the arrester MOA, and the cathode of the eighth thyristor T ₈ are connected as a breaking branch. output terminal.

Further, the DC power supply includes: equivalent inductance L _s of the converter station, equivalent resistance _Rs and equivalent capacitance C _s of the converter station. One end of the equivalent inductance L _s of the converter station is connected to One end of the first mechanical switch S ₁ , the anode of the first diode D ₁ , the cathode of the third diode D ₃ , and the anode of the eleventh thyristor T ₁₁ are connected. The equivalent inductance L _s of the converter station is The other end is connected to one end of the equivalent resistance _Rs of the converter station, and the other end of the equivalent resistance _Rs of the converter station is connected to one end of the equivalent capacitance C _s of the converter station. The equivalent capacitance C of the converter station The other end of _s is grounded.

Further, the overhead line is composed of a smoothing reactor L _dc and a line equivalent resistance R _line . One end of the smoothing reactor L _dc is connected to the anode of the second diode D ₂ and the fourth diode respectively. The negative electrode of D ₄ is connected, the other end of the smoothing reactor L _dc is connected to one end of the line equivalent resistance R _line , and the other end of the line equivalent resistance R _line is grounded.

Further, the bypass branch includes: a thyristor group T _by and a discharge resistor R _by . The cathode of the thyristor group T _by is connected to the output end of the breaking branch. The anode of the thyristor group T _by is connected to the discharge resistor R by. One end of the resistor R _by is connected, and the other end of the energy leakage resistor R _by is connected to the ground.

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

(1) The present invention adds a current-limiting branch and uses the charging and discharging characteristics of the commutation capacitor to realize switching of the current-limiting impedance. When an overhead line fails, the fault current is commutated to the current-limiting branch. The first commutation capacitor Discharge first and then charge. During the discharge process, since the polarity of the first commutation capacitor is opposite to the polarity of the DC power supply, the rising rate of the fault current slows down; during the charging process, the polarity of the first commutation capacitor becomes left positive and right negative. The first thyristor is therefore turned on, the current limiting impedance is put into the loop, and the peak fault current is significantly suppressed;

(2) Since the smoothing reactor is installed on the overhead line to suppress the change of current, the fault current attenuation speed of the DC circuit breaker is slowed down during the breaking process, and the fault isolation time becomes longer. In the present invention, by adding a bypass branch, during the breaking process The energy stored in the smoothing reactor on the fault side is dissipated through the energy leakage resistor in the bypass branch, which significantly shortens the fault isolation time;

(3) Different from the traditional DCCB, the thyristor is used as the main switching device in the breaking branch of the present invention, replacing the expensive full control device IGBT. At the same time, the current is realized through the bridge circuit composed of the first to fourth diode groups. Bidirectional conduction further saves the number of components, effectively reducing costs while ensuring the normal operation of the high-voltage DC circuit breaker.

Description of the drawings

Figure 1 is a frame diagram of a capacitor-type high-voltage DC circuit breaker with current limiting capability according to the present invention;

Figure 2 is a schematic circuit connection diagram of the capacitive high-voltage DC circuit breaker with current limiting capability of the present invention;

Figure 3 is a diagram showing the relationship between the reverse voltage peak value of the first commutation capacitor and the first commutation capacitor C ₁ ;

Figure 4 is a diagram showing the relationship between fault current and first commutation capacitance C ₁ ;

Figure 5 shows the resistance change pattern of the fault current following the current limiting resistor R _L ;

Figure 6 is a graph of the fault current following the reactance change of the current limiting inductor L _L ;

Figure 7 is a precharging circuit diagram of the first commutation capacitor and the second commutation capacitor;

Figure 8 is a schematic diagram of current conduction in the time period from t ₃ to t ₄ ;

Figure 9 is a schematic diagram of current conduction in the time period from t ₄ to t ₅ ;

Figure 10 is a schematic diagram of current conduction in the time period from t ₅ to t ₆ ;

Figure 11 is a schematic diagram of current conduction in the time period from t ₆ to t ₇ ;

Figure 12 is a schematic diagram of current conduction in the time period from t ₇ to t ₈ ;

Figure 13 is a schematic diagram of current conduction in the time period from t ₈ to t ₉ ;

Figure 14 is a schematic diagram of current conduction in the time period from t ₉ to t ₁₀ ;

Figure 15 is a schematic diagram comparing the fault current of the capacitive high-voltage DC circuit breaker of the present invention and the traditional high-voltage DC circuit breaker.

Detailed ways

The technical solution of the present invention will be further explained below with reference to the accompanying drawings.

Figure 1 is a frame diagram of a capacitor-type high-voltage DC circuit breaker with current-limiting capability of the present invention. The capacitor-type high-voltage DC circuit breaker includes: DC power supply, main current branch, current-limiting branch, breaking branch, and bypass. The branch circuit and the overhead line, the DC power supply is connected to the input end of the main current branch circuit, and the output end of the main current branch circuit is connected to the overhead line; the DC power supply is also connected to the input end of the current limiting branch through the first diode D ₁ end is connected, the input end of the current-limiting branch is also connected to the overhead line through the second diode D ₂ , the output end of the current-limiting branch is connected to the input end of the breaking branch, and the output end of the breaking branch is connected to the bypass branch The output end of the breaking branch is also connected to the DC power supply through the third diode D ₃ and the eleventh thyristor T ₁₁ , and the output end of the breaking branch is also connected to the overhead line through the fourth diode D ₄ . When the line is normal, the current of the DC power supply directly flows into the overhead line from the main current branch; when a line fault occurs, the first commutation capacitor C ₁ in the current limiting branch of the present invention ensures that the fifth thyristor T ₅ can be reliably turned off. It breaks the fault current into the current-limiting branch. It has a current-limiting function and can effectively suppress the fault current peak value. At the same time, it discharges energy by breaking the branch and bypassing the branch to shorten the fault isolation time.

In the present invention, the anode of the first diode D ₁ , the cathode of the third diode D ₃ , and the anode of the eleventh thyristor T ₁₁ are all connected to the DC power supply, and the cathode of the first diode D ₁ is connected to the current limiting branch. The input terminal of the branch circuit is connected, the anode of the third diode D ₃ and the cathode of the eleventh thyristor T ₁₁ are connected to the output terminal of the breaking branch; the anode of the second diode D ₂ and the cathode of the fourth diode D The cathodes of ₄ are connected to the overhead lines, the cathode of the second diode D ₂ is connected to the input end of the current limiting branch, and the anode of the fourth diode D ₄ is connected to the output end of the breaking branch. The present invention realizes that the current of the capacitor type high-voltage DC circuit breaker can be conducted in two directions through a bridge circuit composed of first to fourth diodes.

As shown in Figure 2, the main flow branch in the present invention is composed of a first mechanical switch _S1 and a load transfer switch LCS connected in series. One end of the first mechanical switch _S1 is connected to the DC power supply, and the output end of the load transfer switch LCS is connected to the overhead line. ;The load transfer switch LCS consists of two insulated gate bipolar transistors IGBT and two diodes. The emitter of one insulated gate bipolar transistor IGBT is connected to the anode of one diode and the emitter of the other insulated gate bipolar transistor IGBT. pole connection, the collector of one insulated gate bipolar transistor IGBT is connected to the cathode of a diode; the emitter of another insulated gate bipolar transistor IGBT is also connected to the anode of another diode, and the other insulated gate bipolar transistor IGBT is connected to the anode of another diode. The collector of the IGBT is connected to the cathode of another diode.

As shown in Figure 2, the current-limiting branch in the present invention includes: a first commutation capacitor C ₁ , a current-limiting resistor R _L , a current-limiting inductor _LL , a second mechanical switch S ₂ , a self-charging resistor R, and a first thyristor T ₁ , the second thyristor T ₂ , the third thyristor T ₃ , the fourth thyristor T ₄ , the fifth thyristor T ₅ , the sixth thyristor T ₆ and the seventh thyristor T ₇ , the anode of the first thyristor T ₁ , the second thyristor T ₂ The anode and the cathode of the third thyristor T ₃ are connected as the input end of the current limiting branch; the cathode of the first thyristor T ₁ is connected to one end of the current limiting resistor R _L , and the other end of the current limiting resistor R _L is connected to the fourth The cathode of the thyristor T ₄ is connected to one end of the current limiting inductor L _L. The anode of the fourth thyristor T ₄ is connected to the other end of the current limiting inductor L _L. One end of the first commutation capacitor C ₁ is connected to the right plate and the sixth thyristor T ₆ The cathode and the anode of the seventh thyristor T ₇ are connected, and the other end of the left plate of the first commutation capacitor C ₁ is respectively connected to one end of the self-charging resistor R, the cathode of the second thyristor T ₂ , the anode of the third thyristor T ₃ , The anode of the fifth thyristor T ₅ is connected, the other end of the self-charging resistor R is connected to one end of the second mechanical switch S ₂ , and the other end of the second mechanical switch S ₂ is grounded; the cathode of the fifth thyristor T ₅ and the sixth thyristor T The anode of ₆ and the cathode of the seventh thyristor T ₇ are connected as the output end of the current limiting branch and connected to the input end of the breaking branch.

The first commutation capacitor C ₁ in the present invention can ensure that the fifth thyristor T ₅ is reliably turned off and quickly transfer the current to the current limiting branch. When the voltage polarity of the first commutation capacitor C ₁ changes to left positive and right negative, the current limiting impedance R _L is naturally put into the loop; during the energy discharge stage, the first commutation capacitor C ₁ is responsible for absorbing the current limiting inductance L _L The role of residual energy. At the same time, the value of the first commutation capacitor C ₁ also affects the pressure bearing condition of each thyristor. Figure 3 describes the relationship between the reverse voltage peak value of the first commutation capacitor and the first commutation capacitor C _1. It can be seen that, The smaller the value of the first commutation capacitor C ₁ , the greater the reverse voltage peak, the higher the withstand voltage requirements for each thyristor group, and the greater the number of thyristors that need to be connected in series. Therefore, the first commutation capacitor The value of C ₁ cannot be too small. In addition, the size of the first commutation capacitor C ₁ also affects the size of the fault current. In one technical solution of the present invention, the reactances of the current-limiting resistor R _L and the current-limiting inductor L _L are taken to be 15Ω and 200mH respectively, and the fault current is equal to The size relationship of the first commutation capacitor C ₁ is shown in Figure 4. It can be seen that the smaller the capacitance value of the first commutation capacitor C ₁ , the faster the current limiting inductor _LL is put in, and the smaller the fault current peak value. Therefore, from the suppression From the perspective of current peak value, the capacitance value of the first commutation capacitor C ₁ should be as small as possible. Therefore, after comprehensive consideration, the capacitance value of the first commutation capacitor C ₁ in the present invention is taken as 20 μF.

The input of the current-limiting resistor _RL in the present invention can effectively suppress the rising peak value of the second fault current. At the same time, part of the energy released by the current-limiting inductor _LL can be consumed during the energy discharge stage to avoid the occurrence of overcurrent. The fault current changes with the resistance of the current-limiting resistor R _L as shown in Figure 5: The greater the resistance of the current-limiting resistor R _L , the better the current limiting effect of the high-voltage circuit breaker. Therefore, the resistance of the current-limiting resistor R _L should be as high as possible. However, considering that the resistor will generate a large amount of heat in large currents during actual operation, the heat dissipation problem is difficult to ignore. Therefore, the resistance value of the current limiting resistor R _L cannot be increased infinitely. After comprehensive consideration, the resistance value of the current limiting resistor R _L in the present invention is set to 15Ω.

In the present invention, the current limiting inductor _LL is a key component to realize the current limiting function. The input of the current limiting inductor _LL can effectively suppress the rising rate of the fault current, thereby achieving the purpose of current limiting. As shown in Figure 6, the fault current follows the reactance change of the current-limiting inductor L _L. It can be seen that the greater the reactance value of the current-limiting inductor L _L , the faster the fault current attenuates and the lower its secondary current peak value. However, considering At present, the cost of high-voltage impedance is high, and its insulation and safety issues also need to be carefully considered. Therefore, in the present invention, a current-limiting inductor _LL with a reactance value of 150mH is used.

As shown in Figure 2, the breaking branch in the present invention includes: the second commutation capacitor _C2 , the arrester MOA, the eighth thyristor _T8 , the ninth thyristor _T9 and the tenth thyristor _T10 . The second commutation capacitor _C2 One end of the arrester MOA and the anode of the eighth thyristor T ₈ are connected as the input end of the breaking branch and connected to the output end of the current limiting branch; the other ends of the two commutation capacitors C ₂ are respectively connected to the ninth thyristor T The cathode of the ninth thyristor T ₁₀ is connected to the anode of the tenth thyristor T ₁₀ ; the anode of the ninth thyristor T ₉ , the cathode of the tenth thyristor T ₁₀ , the other end of the arrester MOA, and the cathode of the eighth thyristor T ₈ are connected as the output end of the breaking branch . The breaking branch of the present invention adopts thyristor as the main switching device, which can realize the shutdown of fault current and reduce the cost. The setting of the second commutation capacitor _C2 ensures that the arrester MOA is put into the loop as soon as possible to complete the fault isolation. Therefore, the second commutation The time for capacitor C ₂ to charge to the arrester MOA operating voltage should be as short as possible. Therefore, the value of the second commutation capacitor C ₂ cannot be too large, and the forward charging voltage and capacitance value of the second commutation capacitor C ₂ are negative. Relatedly, if the value is too small, the forward voltage peak of the second commutation capacitor C ₂ will be too large, thereby increasing the insulation requirements for the thyristor group. After comprehensive consideration, the value of the second commutation capacitor C ₂ is 5μF.

As shown in Figure 2, the DC power supply in the present invention includes: equivalent inductance L _s of the converter station, equivalent resistance _Rs and equivalent capacitance C _s of the converter station. One end of the equivalent inductance L _s of the converter station is connected to One end of the first mechanical switch S ₁ , the anode of the first diode D ₁ , the cathode of the third diode D ₃ , and the anode of the eleventh thyristor T ₁₁ are connected, and the other end of the equivalent inductance L _s of the converter station is connected. It is connected to one end of the equivalent resistance _Rs of the converter station, the other end of the equivalent resistance _Rs of the converter station is connected to one end of the equivalent capacitance C _s of the converter station, and the other end of the equivalent capacitance C _s of the converter station is connected to the ground.

As shown in Figure 2, the overhead line in the present invention is composed of a smoothing reactor L _dc and a line equivalent resistance R _line . One end of the smoothing reactor L _dc is connected to the anode of the second diode D ₂ and the fourth diode respectively. The negative pole of D ₄ is connected, the other end of the smoothing reactor L _dc is connected to one end of the line equivalent resistance R _line , and the other end of the line equivalent resistance R _line is grounded.

As shown in Figure 2, the bypass branch in the present invention includes: a thyristor group T _by and a leakage resistor R _by . The cathode of the thyristor group T _by is connected to the output end of the breaking branch. The anode of the thyristor group T _by is connected to the leakage resistor R by. One end of _by is connected, and the other end of the energy leakage resistor R _by is connected to the ground. During the breaking process, the energy stored in the smoothing reactor on the fault side is dissipated through the energy leakage resistor R _by in the bypass branch, which significantly shortens the fault isolation time.

The working process of the capacitive high-voltage DC circuit breaker with current-limiting energy of the present invention has four stages: steady-state operation process, current-limiting process, breaking process and bypass energy-discharging process.

In the steady-state operation process (t ₀ ~ t ₂ ), in the stage t ₀ ~ t ₁ , the first commutation capacitor C ₁ and the second commutation capacitor C ₂ need to be precharged, and the conduction is triggered at time t ₀ The sixth thyristor T ₆ , the ninth thyristor T ₉ , and the eleventh thyristor T ₁₁ are connected, and the second mechanical switch S ₂ is closed. The current flows through the DC power supply through the eleventh thyristor T ₁₁ , the ninth thyristor T ₉ , and the second switch The energizing loop formed by the capacitor C ₂ , the sixth thyristor T ₆ , the first commutation capacitor C ₁ , the self-charging resistor R and the second mechanical switch S ₂ is shown in Figure 7. The first commutation capacitor C 1 is supplied to the first commutation capacitor C ₁ through the DC power supply. , the second commutation capacitor C ₂ is charged. After the charging is completed, the thyristor is automatically turned off and the second mechanical switch S ₂ is disconnected. After the charging is completed, the voltage of the first commutation capacitor _C1 and the voltage of the second commutation capacitor U _{C2 are} They are:

Among them, U _dc represents the DC bus voltage;

In the t ₁ to t ₂ stage, the high-voltage DC circuit breaker operates normally, the first mechanical switch S ₁ and the load transfer switch LCS are turned on, and the current flows through the main current branch. Since the main branch only has two IGBTs connected in series, Low pass-state loss.

In the current limiting process (t ₂ ~ t ₇ ), first at time t ₂ , a short-circuit fault occurs on the overhead line, and the DC current rises rapidly. At this time, the DCCB does not act, and the current still flows through the main through-flow branch. At time t ₃ , the system detects an overcurrent phenomenon in the line, and DCCB starts to act: triggering the conduction of the second thyristor T ₂ , the fifth thyristor T ₅ and the eighth thyristor T ₈ , and the load transfer switch LCS immediately after receiving the shutdown signal Turn off, the first mechanical switch _S1 starts to act. Therefore, the current conduction path during the time period t ₃ ~ t ₄ is as shown in Figure 8: the DC power flows through the first diode D ₁ , the second thyristor T ₂ , the fifth thyristor T ₅ , and the eighth thyristor T ₈ , the fourth diode D ₄ goes to the overhead line. Therefore, in the time period t ₂ ~ t ₄ , the expression of the fault line current i _dc is:

Among them, I ₀ is the steady-state current value of the DC line, τ ₁ represents the circuit discharge time constant, τ ₁ =(L _s +L _dc )/R _s .

During the time period from t ₄ to t ₅ , the first mechanical switch S ₁ reaches the rated opening distance and is triggered to turn on the seventh thyristor T ₇ . The first commutation capacitor C ₁ begins to discharge, and the fifth thyristor T ₅ is turned off due to the back pressure. , the current flowing through the fifth thyristor T ₅ is transferred to the seventh thyristor T ₇ . The current path during this period is as shown in Figure 9: the current of the DC power supply flows through the first diode D ₁ , the second thyristor T ₂ , the first The commutation capacitor C ₁ , the seventh thyristor T ₇ , the eighth thyristor T ₈ , and the fourth diode D ₄ are connected to the overhead line.

In the time period from t ₄ to t ₅ , the state equation of the first commutation capacitor C ₁ is:

Ignoring the time of current transfer, it can be considered that all the current is transferred to the branch where the first commutation capacitor C ₁ is located at time t _4. Suppose the precharge voltage of the first commutation capacitor C ₁ is U _C1 , let i ₂ (t ₄ ) =i _dc (t ₄ )=I ₂ , θ=arctan(ω/A ₁ ), substituted into equation (3), we can get:

Among them: i ₂ represents the current of the branch where the first commutation capacitor is located, and u _C1 represents the voltage of the first commutation capacitor.

At time t ₅ , the discharge of the first commutation capacitor C ₁ ends. During the time period from t ₅ to t ₆ , reverse charging begins. The first thyristor T ₁ conducts due to withstanding the forward voltage, and the current limiting resistor and current limiting inductor are put in. In the fault loop, the current flowing through the capacitor gradually decreases. The current path in the time period from t ₅ to t ₆ is shown in Figure 10: The current of the DC power supply flows through the first diode D ₁ and through the first thyristor T ₁ and After the parallel branch of the current-limiting resistor _RL , the current-limiting inductor _LL , the second thyristor _T2 , and the first commutation capacitor _C1 , the seventh thyristor _T7 , the eighth thyristor _T8 , and the fourth diode D ₄ flows into overhead lines.

The circuit differential equation in this process is:

Simplified:

Among them, L _∑ =L _s +L _dc +L _L .

Set the initial conditions u _c1 (t ₅ ) = 0, i ₂ (t ₅ ) = I ₃ , let Substituting into equation (6), we get:

During the time period t ₆ ~ t ₇ , as the voltage of the first commutation capacitor C ₁ reaches the system voltage, the second thyristor T ₂ is naturally turned off, and the current limiting resistor and current limiting inductor are completely put into the fault circuit. The specific current The flow path is shown in Figure 11: the current of the DC power supply flows through the first diode D ₁ , the first thyristor T ₁ , the current limiting resistor R _L , the current limiting inductor L _L , the seventh thyristor T ₇ , the eighth thyristor T ₈ , The fourth diode D ₄ goes into the overhead line. It is known that i _dc (t ₆ ) = i ₃ (t ₆ ) = I ₄ , then the instantaneous current i _dc of the DC bus is:

Among them, the circuit discharge time constant τ ₂ =(L _s +L _dc +L _L )/(R _s +R _L ).

In the breaking process (t ₇ ~ t ₁₀ ), first, in the time period t ₇ ~ t ₈ , the protection system completes the fault determination, the circuit breaker receives the tripping command, turns on the tenth thyristor T ₁₀ , and the eighth thyristor T ₈ is turned on due to Withstand the back pressure and turn off, the second commutation capacitor C ₂ begins to discharge. The current flow path during this period is shown in Figure 12: the current of the DC power supply flows through the first diode D ₁ , the first thyristor T ₁ , the limiter The current resistor R _L , the current limiting inductor _LL , the seventh thyristor T ₇ , the second commutation capacitor C ₂ , the tenth thyristor T ₁₀ , and the fourth diode D ₄ are connected to the overhead line. Let i ₄ (t ₇ )=i _dc (t ₇ )=I ₅ , the state equation of the second commutation capacitor C ₂ is:

In the t ₈ ~ t ₉ stage, the second commutation capacitor C ₂ is charged to the system voltage, the current begins to decay, the voltage at both ends of the current limiting inductor L _L becomes positive down and negative up, the fourth thyristor T ₄ is turned on, and the current limiting inductor L _L is bypassed. The current flow path at this stage is as shown in Figure 13: The current of the DC power supply flows through the first diode D ₁ , the first thyristor T ₁ , the current limiting resistor R _L , the fourth thyristor T ₄ , the seventh The thyristor T ₇ , the second commutation capacitor C ₂ , the tenth thyristor T ₁₀ and the fourth diode D ₄ are connected to the overhead line.

In the t ₉ to t ₁₀ stage, the second commutation capacitor C ₂ is charged to the arrester MOA action voltage, the arrester MOA is turned on, triggering the conduction thyristor group T _by , the energy on the fault side is released through the bypass branch, and the current flows during this period The path is as shown in Figure 14: The current of the DC power supply flows through the first diode D ₁ , the first thyristor T ₁ , the current limiting resistor R _L , the fourth thyristor T ₄ , the seventh thyristor T ₇ , the arrester MOA, and the fourth diode. tube D ₄ to the overhead line; at the same time, the freewheeling current in the smoothing reactor forms a energizing loop through the energy leakage resistor R _by , the thyristor group T _by , and the fourth diode D ₄ . Assuming that the voltage across the arrester is always the rated voltage U _MOV during the operation of the arrester, the DC current during the breaking time is:

Among them, the circuit discharge time constant τ ₃ =L _s /(R _s +R _L ).

Solving the above equation we get:

It can be seen from formula (11) that since the inductors L _L and L _dc are bypassed, the time constant is reduced and the fault current can decay to zero faster.

In the bypass energy dissipation process (t>t ₁₀ ), when the second commutation capacitor _C2 is charged to the system voltage, the current begins to decay, and the voltage at both ends of the current-limiting inductor L _L becomes positive below and negative above, and the fourth thyristor T ₄ is turned on due to the forward voltage drop, and the fourth thyristor is bypassed; when the second commutation capacitor C ₂ is charged to the arrester MOA action voltage, the conduction thyristor group T _by is triggered, and the energy stored in the fault side reactance passes through the discharge Energy resistance R _by dissipation.

As shown in Figure 15, compared with the traditional DCCB, the fault current peak value of the capacitor type high-voltage DC circuit breaker of the present invention is reduced by 34.85%, the fault isolation time is shortened by 11.92%, and it has good current limiting effect, fast fault isolation speed and economy. Better advantages.

The above are only the preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above-mentioned embodiments. All technical solutions that fall under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, several improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (9)

1. A capacitive high-voltage DC circuit breaker with current limiting capability, which is characterized in that it includes: a DC power supply, a main current branch, a current limiting branch, a breaking branch, a bypass branch and an overhead line, said The DC power supply is connected to the input end of the main current branch, and the output end of the main current branch is connected to the overhead line; the DC power supply is also connected to the input end of the current limiting branch through the first diode D ₁ , the input end of the current limiting branch is also connected to the overhead line through the second diode D ₂ , the output end of the current limiting branch is connected to the input end of the breaking branch, and the output end of the breaking branch It is connected to the bypass branch. The output end of the breaking branch is also connected to the DC power supply through the third diode D ₃ and the eleventh thyristor T ₁₁ . The output end of the breaking branch is also connected to the DC power supply through the fourth diode. Pipe D ₄ is connected to overhead lines; When the line is normal, the current of the DC power supply directly flows into the overhead line from the main current branch; when a line fault occurs, the current limiting branch of the present invention realizes the turn-off of the fifth thyristor T ₅ through the first commutation capacitor C ₁ , The fault current is commutated into the current-limiting branch, and energy is discharged through the breaking branch and the bypass branch. 2. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 1, characterized in that the main current branch is composed of a first mechanical switch _S1 and a load transfer switch LCS connected in series, and the One end of the first mechanical switch _S1 is connected to the DC power supply, and the output end of the load transfer switch LCS is connected to the overhead line. 3. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 2, characterized in that the load transfer switch LCS is composed of two insulated gate bipolar transistors IGBT and two diodes, one The emitter of the insulated gate bipolar transistor IGBT is connected to the anode of a diode and the emitter of another insulated gate bipolar transistor IGBT, and the collector of one insulated gate bipolar transistor IGBT is connected to the cathode of a diode; the other The emitter of one insulated gate bipolar transistor IGBT is also connected to the anode of another diode, and the collector of the other insulated gate bipolar transistor IGBT is connected to the cathode of another diode. 4. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 1, characterized in that the anode of the first diode _D1 , the cathode of the third diode D3, and the cathode of the third diode _D3 . The anodes of the eleven thyristors T ₁₁ are connected to the DC power supply, the cathode of the first diode D ₁ is connected to the input end of the current limiting branch, the anode of the third diode D ₃ and the eleventh thyristor The cathode of T ₁₁ is connected to the output end of the breaking branch; the anode of the second diode D ₂ and the cathode of the fourth diode D ₄ are both connected to the overhead line, and the second diode D ₂ The negative electrode of is connected to the input end of the current limiting branch, and the positive electrode of the fourth diode D ₄ is connected to the output end of the breaking branch. 5. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 4, characterized in that the current limiting branch includes: a first commutation capacitor C ₁ , a current limiting resistor R L , a limiting resistor R _L Current inductor L _L , second mechanical switch S ₂ , self-charging resistor R, first thyristor T ₁ , second thyristor T ₂ , third thyristor T ₃ , fourth thyristor T ₄ , fifth thyristor T ₅ , sixth thyristor T ₆ and the seventh thyristor T ₇ , the anode of the first thyristor T ₁ , the anode of the second thyristor T ₂ , and the cathode of the third thyristor T ₃ are connected as the input end of the current limiting branch; the first thyristor The cathode of T ₁ is connected to one end of the current limiting resistor _RL , and the other end of the current limiting resistor _RL is connected to the cathode of the fourth thyristor T ₄ and one end of the current limiting inductor _LL respectively. The fourth thyristor T ₄ The anode of , the other end of the current limiting inductor _LL , the right plate of the first commutation capacitor C ₁ , the cathode of the sixth thyristor T ₆ , and the anode of the seventh thyristor T ₇ are connected. The first commutation capacitor C ₁ The left plate of is connected to one end of the self-charging resistor R, the cathode of the second thyristor _T2 , the anode of the third thyristor _T3 , and the anode of the fifth thyristor _T5 . The other end of the self-charging resistor R is connected to the second One end of the mechanical switch _S2 is connected, and the other end of the second mechanical switch _S2 is connected to ground; the cathode of the fifth thyristor _T5 , the anode of the sixth thyristor _T6 , and the cathode of the seventh thyristor _T7 are connected as limiters. The output end of the flow branch is connected to the input end of the breaking branch. 6. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 5, characterized in that the breaking branch includes: a second commutation capacitor C ₂ , a lightning arrester MOA, and an eighth thyristor T ₈ , the ninth thyristor T ₉ and the tenth thyristor T ₁₀ , one end of the second commutation capacitor C ₂ , one end of the arrester MOA, and the anode of the eighth thyristor T ₈ are connected as the input end of the breaking branch, and are connected with the current limiting The output end of the branch is connected; the other ends of the two commutation capacitors _C2 are respectively connected with the cathode of the ninth thyristor _T9 and the anode of the tenth thyristor _T10 ; the anode of the ninth thyristor _T9 and the tenth thyristor The cathode of T ₁₀ , the other end of the arrester MOA, and the cathode of the eight-thyristor T ₈ are connected as the output end of the breaking branch. 7. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 6, characterized in that the DC power supply includes: a converter station equivalent inductance L _s and a converter station equivalent resistance R _s and the equivalent capacitance C _s of the converter station. One end of the equivalent inductance L _s of the converter station is connected to one end of the first mechanical switch S ₁ , the anode of the first diode D ₁ , and the third diode D ₃ respectively. The negative electrode of the converter station is connected to the anode of the eleventh thyristor T _11. The other end of the equivalent inductance L _s of the converter station is connected to one end of the equivalent resistance _Rs of the converter station. The equivalent resistance _Rs of the converter station is The other end is connected to one end of the equivalent capacitance C _s of the converter station, and the other end of the equivalent capacitance C _s of the converter station is connected to the ground. 8. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 6, characterized in that the overhead line is composed of a smoothing reactor L _dc and a line equivalent resistance R _line . One end of the smoothing reactor L _dc is connected to the anode of the second diode D ₂ and the cathode of the fourth diode D ₄ respectively, and the other end of the smoothing reactor L _dc is connected to one end of the line equivalent resistance R _line Connect the other end of the line equivalent resistance R _line to ground. 9. A capacitive high-voltage DC circuit breaker with current limiting capability according to claim 6, characterized in that the bypass branch includes: a thyristor group T _by and a leakage resistor R _by , and the thyristor group The cathode of T _by is connected to the output end of the breaking branch, the anode of the thyristor group T _by is connected to one end of the energy leakage resistor R _by , and the other end of the energy leakage resistor R _by is grounded.