CN118693757A - A combined DC circuit breaker reclosing auxiliary device and parameter design method thereof - Google Patents

Abstract

The invention provides a combined type direct current breaker reclosing auxiliary device and a parameter design method thereof, relating to the field of flexible direct current transmission, and comprising a bidirectional thyristor, a voltage regulating resistor and a protection inductor; the resonant branch is provided with a resonant capacitor, the bidirectional thyristor is connected with the voltage regulating resistor in series, the voltage regulating resistor is connected with the protection inductor in series, and the bidirectional thyristor is connected with the voltage regulating resistor and the protection inductor in series and then is connected with the resonant capacitor on the resonant branch in parallel as a steering loop. After one-time switching-off is completed, the residual voltage of the resonant capacitor is utilized to carry out reversing and adjusting through a steering loop, so that a second set of transfer branches required by reclosing are saved. When permanent fault occurs, the high-frequency reverse current can be directly output through voltage adjustment and overlapped with the short-circuit current, so that the permanent fault current can be quickly and reliably switched on and off. In addition, the optimal element parameter value is determined through constraint conditions, and a reliable parameter design method is provided for a reclosing auxiliary device of the combined direct current breaker.

Description

A combined DC circuit breaker reclosing auxiliary device and parameter design method thereof

Technical Field

The present invention relates to the field of flexible direct current power transmission, and in particular to a combined direct current circuit breaker reclosing auxiliary device and a parameter design method thereof.

Background Art

In recent years, medium and high voltage direct current transmission systems have been widely used due to their long distance and large transmission capacity. In addition, the development of DC power grids has enhanced the flexibility of distributed green energy access to the power grid, eliminating complex current conversion devices, and playing an important role in sustainable energy utilization. Since the DC power grid has no natural zero-crossing point of current and the fault develops quickly, the difficulty of breaking a DC circuit breaker is much greater than that of an AC circuit breaker of the same voltage level. Therefore, DC breaking technology has become an important factor restricting the further development of DC power grids.

At present, DC circuit breakers can be roughly divided into three categories according to the key breaking components and principles: mechanical DC circuit breakers, all-solid-state DC circuit breakers and hybrid DC circuit breakers. Each type of DC circuit breaker has different implementation forms and topological structures. Mechanical DC circuit breakers have low cost and large breaking capacity. They achieve DC breaking by creating an artificial zero crossing point for the mechanical switch of the traditional AC circuit breaker.

Although DC circuit breakers have good performance, the manufacturing cost of DC circuit breakers is much higher than that of AC circuit breakers. With the continuous increase in the capacity of multi-terminal flexible DC transmission, the investment in equipment has become one of the constraints restricting its development. To solve this problem, it is proposed to realize the interruption of fault current by sharing the main disconnecting switch on a busbar to reduce the number and investment cost of DC circuit breakers in the DC power grid. In addition, since temporary faults in flexible DC transmission account for the majority, the fast reclosing function of DC circuit breakers can quickly restore power supply and effectively improve the reliability of power supply. However, existing studies often ignore the reclosing problem when proposing new mechanical DC circuit breaker topologies, resulting in the inability to put the theory into practice. Even if some schemes propose a reclosing strategy, because after the mechanical DC circuit breaker consumes energy, the voltage polarity on the capacitor is opposite to the fault direction, the voltage is large, and the line cannot be directly closed by closing the switch on the line to restore normal operation, so as to achieve the purpose of fast and reliable power restoration. In addition, a second branch needs to be installed, which is redundant and cumbersome and has poor economic efficiency.

Summary of the invention

In order to solve the technical problem that a second branch needs to be installed for a mechanical DC circuit breaker reclosing, which increases the cost, the present invention provides a combined DC circuit breaker reclosing auxiliary device, comprising a DC circuit breaker, a plurality of current-carrying branches, an energy absorption branch and a resonance branch, a bidirectional thyristor, a voltage-regulating resistor and a protective inductor; a resonant capacitor is provided on the resonance branch, the bidirectional thyristor is connected in series with the voltage-regulating resistor, the voltage-regulating resistor is connected in series with the protective inductor, and the bidirectional thyristor, the voltage-regulating resistor and the protective inductor are connected in series as a steering circuit and connected in parallel with the resonant capacitor on the resonance branch.

Furthermore, the bidirectional thyristor is used to adjust the voltage polarity on the resonant capacitor; the voltage regulating resistor is used to adjust the voltage of the resonant capacitor after the disconnection is completed; the protective inductor is used to protect the thyristor to prevent the bidirectional thyristor from being damaged by excessive instantaneous current change rate.

Furthermore, after the DC circuit breaker is disconnected, the bidirectional thyristor is turned on, and its current direction is the same as the fault current direction, so as to reverse the voltage polarity on the resonant capacitor and adjust the voltage on the resonant capacitor by modifying the voltage regulating resistor and the protection inductor value.

A parameter design method for a combined DC circuit breaker reclosing auxiliary device comprises the following steps:

Step 1: Selection of bidirectional thyristor;

Step 2: Obtain the value range of the protection inductance through the instantaneous current rise rate of the bidirectional thyristor;

Step 3: According to the arc at the break of the fast mechanical switch and the maximum current peak value to obtain the voltage regulating resistance range, Indicates the maximum instantaneous rate of change of current flowing through the bidirectional thyristor;

Step 4: Obtain the optimal values of component parameters by enumeration method with the maximum total energy on the resonant capacitor of the combined DC circuit breaker as the optimization target.

Furthermore, the selection method of the bidirectional thyristor in step 1 is: , Indicates the maximum instantaneous current change rate allowed when the bidirectional thyristor is turned on.

Furthermore, the selection method of the voltage regulating resistor and the protection inductor in step 2 and step 3: the resonant capacitor, the voltage regulating resistor and the protection inductor need to satisfy the following relationship:

,

In the formula, is the voltage regulating resistor, To protect the inductor, is the resonant capacitor.

Furthermore, the enumeration method in step 4 uses step 1, step 2 and step 3 as three constraints to obtain the minimum value of the protection inductor, the maximum value and the minimum value of the voltage regulating resistor. Based on the minimum value of the protection inductor, the step size is set to obtain the maximum voltage on the resonant capacitor.

Beneficial effects: The present invention proposes a reclosing auxiliary device and a parameter design method for a combined DC circuit breaker. After a disconnection is completed, the residual voltage of the resonant capacitor is used to perform commutation and adjustment through a steering circuit, saving the second set of transfer branches required for the reclosing. In the event of a permanent fault, the high-frequency reverse current can be directly output through voltage adjustment and superimposed on the short-circuit current to quickly and reliably disconnect the permanent fault current. In addition, the optimal component parameter value is determined through constraint conditions, providing a reliable parameter design method for the reclosing auxiliary device of the combined DC circuit breaker.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a topological structure diagram of a combined DC circuit breaker in Embodiment 1 of the present invention;

2 is a schematic diagram of the action sequence, currents in each branch, and voltage of the energy-absorbing branch of the combined DC circuit breaker in the second embodiment of the present invention when a temporary fault occurs;

3 is a schematic diagram of the action sequence, currents in each branch, and voltage of the energy-absorbing branch of the combined DC circuit breaker in the second embodiment of the present invention when a permanent fault occurs;

4 is a flow chart of a parameter design method for a combined DC circuit breaker reclosing auxiliary device in Embodiment 2 of the present invention;

FIG. 5 is a waveform diagram of the voltage and energy on the resonant capacitor under the parameter design method in the second embodiment of the present invention.

DETAILED DESCRIPTION

In order to describe the present invention more specifically, the following drawings and specific implementation schemes are used to describe the technical solution of the present invention in detail.

Embodiment 1

Embodiment 1 of the present invention provides a combined DC circuit breaker reclosing auxiliary device, including a DC circuit breaker, a plurality of current-carrying branches, an energy absorption branch and a resonant branch, a bidirectional thyristor, a voltage-regulating resistor and a protective inductor; a resonant capacitor is provided on the resonant branch, the bidirectional thyristor is connected in series with the voltage-regulating resistor, the voltage-regulating resistor is connected in series with the protective inductor, and the bidirectional thyristor, the voltage-regulating resistor and the protective inductor are connected in series as a steering circuit and connected in parallel with the resonant capacitor on the resonant branch.

The through-current branch is used to transmit the rated working current and break the short-circuit current on the line, so as to realize the bidirectional flow of the line current. A plurality of through-current branches (LSR_1, LSR_2, ..., LSR_ m ) correspond to the inlet and outlet on each branch, the midpoint of the LSR is the electrical port (port 2, ..., port m ) of the combined DC circuit breaker, and the currents are respectively I ₂ , ..., I _m , and at the same time, each midpoint divides each through-current branch into an upper bridge arm and a lower bridge arm, the upper bridge arm is connected to a busbar Bus, and the lower bridge arms are connected to each other, each upper bridge arm is composed of a fast mechanical opening switch (Kf_1, Kf_2 ..., Kf_ m ), and the currents passing through the fast mechanical opening switch are respectively ( I _f1 , I _f1 ..., I _{f m} ), and each lower bridge arm is composed of a fast mechanical closing switch (Kh_1, Kh_2 ..., Kh_ m ), and the fast opening mechanical switch on the through-current branch can only be turned off by arc extinguishing when the short-circuit current passes through zero.

The energy absorption branch is connected in parallel with the current-passing branch. The energy absorption branch is formed by a lightning arrester MOV and is used to discharge the short-circuit current and the energy accumulated on the resonant capacitor during the breaking process. The absorption current is I _mov .

The resonant branch is connected in parallel with the current branch and the energy absorption loop. The resonant branch is composed of an excitation module, a resonant capacitor C ₀ , a resonant inductor L ₀ , a stray resistor R ₀ and a steering loop. C ₀ and MOV are the core components for the resonant branch to establish a transient interruption voltage (TIV) and realize current interruption, and the resonant current is I _C . The excitation module is composed of a pre-charge capacitor C ₁ and an H-bridge submodule. Among them, the H-bridge submodule is composed of 4 integrated gate commutation thyristors (IGCT) (T ₁ , T ₂ , T ₃ , T ₄ ), each IGCT is anti-parallel connected with a freewheeling diode, and the H-bridge submodule is used to generate a resonant current with an increased amplitude, so that the current to be disconnected is transferred to the resonant branch. When the excitation module is turned on, _C0 and _C1 are connected in series, and in order to reduce the withstand voltage of the charging system, the capacitance of _C1 should be much larger than _C0 . The initial voltage of _C1 is _UE , and the entire excitation module is used to realize resonant commutation. The steering circuit is composed of a bidirectional thyristor (S1, S2), a protective inductor _L1 and a voltage regulating resistor _R1. The bidirectional thyristor is used to adjust the voltage polarity on the resonant capacitor, the inductor _L1 is used to protect the thyristor to prevent the instantaneous current change rate from being too large and causing damage to the thyristor, and the voltage regulating resistor _R1 is used to adjust the voltage of _C0 after the interruption is completed. After the DC circuit breaker is disconnected, the bidirectional thyristor is turned on, and its current direction is the same as the fault current direction, which is used to swap the voltage polarity on the resonant capacitor. The voltage on the resonant capacitor is adjusted by modifying the voltage regulating resistor and the protective inductor value.

Embodiment 2

The action sequence of the combined DC circuit breaker is shown in Figure 2. If a temporary fault occurs at port 2, the details are as follows:

The action sequence of the current-carrying branch, resonant branch and energy-absorbing branch of the combined DC circuit breaker after a temporary fault occurs, and the response action time of the control module and the fast mechanical switch are as follows:

At this moment, the DC line operates normally;

At the moment, the DC circuit breaker receives the opening command, the moving and static contacts of the corresponding fast mechanical opening switch Kf on the fault line arc and separate, the current is If _, and the corresponding fast mechanical closing switch Kh on the fault line closes;

At this moment, the fast mechanical opening switch Kf reaches the safe opening distance, and Kh is closed in place at this time. It is triggered according to the preset trigger signal. When the natural frequency in the resonant circuit is equal to the trigger signal frequency, a resonant circuit with increased amplitude can be generated.

At the moment, the current on the flow branch passes through zero under the superposition of the resonant current, the fast mechanical opening switch Kf extinguishes the arc, and all the current is transferred to the resonant branch, and the resonant capacitor _C0 is charged, and the voltage is Vc;

At the moment, the voltage across the resonant branch reaches the threshold voltage across the arrester, the arrester transfers from the high-resistance state to the low-resistance state, the current transfers to the energy absorption branch, and the current I _dc gradually decays and decreases;

At this moment, when the breaking process is completed, the switch Kh is opened, and the two ends of the resonant capacitor are reversed. At this time, the thyristor on the voltage regulating circuit is immediately turned on, and the resonant capacitor is discharged through the underdamped voltage regulating circuit. The voltage is reversed and adjusted to a suitable voltage value, waiting for the reclosing switch to break;

After a waiting time of tens to hundreds of milliseconds, the DC circuit breaker will reclose. If the system determines that the line fault is a temporary fault, the reclosing is successful, the energy is fed back to the pre-charge capacitor, and the system resumes operation.

As shown in FIG3 , the action sequence of the combined DC circuit breaker is shown in FIG3 . If a permanent fault occurs at port 2, the details are as follows:

The action sequence of the current-carrying branch, resonant branch and energy-absorbing branch of the combined DC circuit breaker after a permanent fault occurs, and the response action time of the control module and the fast mechanical switch are as follows:

At this moment, the DC line operates normally;

At the moment, the DC circuit breaker receives the opening command, the moving and static contacts of the fast mechanical opening switch Kf arc and separate, the current is If _, and the fast mechanical closing switch Kh closes;

At this moment, the fast mechanical opening switch Kf reaches the safe opening distance, and Kh is closed in place at this time. It is triggered according to the preset trigger signal. When the natural frequency in the resonant circuit is equal to the trigger signal frequency, a resonant circuit with increased amplitude can be generated.

At the moment, the current on the flow branch passes through zero under the superposition of the resonant current, the fast mechanical opening switch Kf extinguishes the arc, and all the current is transferred to the resonant branch, and the resonant capacitor _C0 is charged, and the voltage is Vc;

At the moment, the voltage across the resonant branch reaches the threshold voltage across the arrester, the arrester transfers from the high-resistance state to the low-resistance state, the current transfers to the energy absorption branch, and the current I _dc gradually decays and decreases;

At this moment, when the breaking process is completed, the switch Kh is opened, and the two ends of the resonant capacitor are reversed. At this time, the thyristor on the voltage regulating circuit is immediately turned on, and the resonant capacitor is discharged through the underdamped voltage regulating circuit. The voltage is reversed and adjusted to a suitable voltage value, waiting for the reclosing switch to break;

At this moment, after a system waiting time of tens to hundreds of milliseconds, the DC circuit breaker recloses. If the system determines that the line fault is a permanent fault, the closed switch Kh generates a high-frequency current opposite to the fault current, and the fast-opening mechanical switch crosses zero and extinguishes the arc, and the fault line at port 2 is successfully isolated.

As shown in FIG4 , the present invention provides a combined DC circuit breaker reclosing auxiliary device and parameter design thereof in the above-mentioned embodiment 1, and the specific process is as follows:

The optimal component parameter value is determined by taking the following steps as constraint conditions. First, the thyristor device is selected, and the instantaneous maximum allowable current rise rate of the existing commercial thyristor is 200A/us. Secondly, the value range of the protection inductor is obtained through the characteristics of the thyristor. Then, the protection resistor is selected through a second-order underdamped circuit. Finally, the energy on the resonant capacitor is used as the optimization target through enumeration method to obtain the optimal solution. The present invention provides a reliable parameter design method for the reclosing device and parameter selection of the combined DC circuit breaker.

To ensure that the thyristor can operate reliably and safely, , It indicates the maximum instantaneous current change rate allowed when the thyristor is turned on. Indicates the maximum instantaneous rate of change of current flowing through the thyristor.

To ensure the normal voltage regulation of the resonant capacitor, the resonant capacitor, the voltage regulating resistor and the protection inductor need to satisfy the following relationship:

,

In the formula, is the voltage regulating resistor, To protect the inductor, is the resonant capacitor.

The specific simulation process of the combined DC circuit breaker reclosing device and its parameter design provided in the second embodiment of the present invention adopts the following example:

Taking a combined DC circuit breaker with a rated voltage of 50kV, a rated current of 2kA, and a maximum breaking current of 30kA as an example, the optimization goal is to make the residual energy on the resonant capacitor as large as possible to ensure that the excess energy can be fed back to the pre-charge voltage, thereby reducing energy loss. There are three constraints in total:

Step 1, as constraint 1: To protect the thyristor, the maximum instantaneous current change rate must not exceed its allowable maximum;

Step 2, as constraint 2: To meet the full current breaking under different working conditions, it is necessary to break the peak current under high current and also meet the switch break under low current. ;

Step 3, as constraint condition 3: To ensure the voltage under the resonant capacitor voltage regulation loop, the second-order circuit should be in an underdamped state and not in an overdamped state.

By taking steps 1, 2 and 3 as three constraints, the minimum value of the protection inductor, the maximum and minimum values of the voltage regulating resistor are obtained. Based on the minimum value of the protection inductor, the maximum voltage on the resonant capacitor can be obtained by setting the step size.

According to step 1, the existing thyristor can withstand 200A/us. , the minimum value of the protection inductor is 200uH.

According to step 2, the value of the voltage regulating resistor must not be less than 0.13Ω.

Assuming the resonant capacitor is known to be 150uF, according to step 3, , it can be seen that the value of the voltage regulating resistor shall not be greater than 1.73Ω.

Finally, by enumeration method, starting from the protection inductor of 200uH and increasing by 10uH as a step size, the optimal values of the residual voltage and residual energy on the resonant capacitor _C0 corresponding to the change of the resonant inductance can be obtained as shown in Table 1 below.

Table 1

Protection inductance (mH) 0.2 0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.28 0.29 0.3 Residual voltage (kV) 16.4 16.5 16.6 16.7 16.8 16.9 16.9 16.7 16.6 16.5 16.3 Residual energy (kJ) 20.2 20.4 20.7 20.9 21.2 21.5 21.4 21.1 20.8 20.4 19.9

Finally, the optimal parameters with the maximum residual energy as the optimization target are shown in Figure 5. The residual voltage and residual energy diagram under different protection inductors. From Figure 5, it can be seen that the protection inductance is 0.25mH, the corresponding residual voltage is 16.9kV, and the residual energy is 21.5kJ, which are the optimal parameters under the optimization target.

Claims (7)

1. A combined DC circuit breaker reclosing auxiliary device, comprising a DC circuit breaker, a plurality of current-carrying branches, an energy-absorbing branch and a resonant branch, characterized in that it also comprises: a bidirectional thyristor, a voltage-regulating resistor and a protective inductor; A resonant capacitor is arranged on the resonant branch, a bidirectional thyristor is connected in series with a voltage regulating resistor, and the voltage regulating resistor is connected in series with a protective inductor. The bidirectional thyristor is connected in series with the voltage regulating resistor and the protective inductor as a steering loop in parallel with the resonant capacitor on the resonant branch. 2. A combined DC circuit breaker reclosing auxiliary device according to claim 1, characterized in that: The bidirectional thyristor is used to adjust the voltage polarity on the resonant capacitor; The voltage regulating resistor is used to adjust the voltage of the resonant capacitor after the disconnection is completed; The protection inductor is used to protect the thyristor to prevent the instantaneous current change rate from being too large and causing damage to the bidirectional thyristor. 3. A combined DC circuit breaker reclosing auxiliary device according to claim 2, characterized in that after the DC circuit breaker is disconnected, the bidirectional thyristor is turned on, and its current direction is the same as the fault current direction, so as to reverse the voltage polarity on the resonant capacitor and adjust the voltage on the resonant capacitor by modifying the voltage regulating resistor and the protective inductor value. 4. A parameter design method applicable to the combined DC circuit breaker reclosing auxiliary device according to claim 1, 2 or 3, characterized in that it comprises the following steps: Step 1: Selection of bidirectional thyristor; Step 2: Obtain the value range of the protection inductance through the instantaneous current rise rate of the bidirectional thyristor; Step 3: According to the arc at the break of the fast mechanical switch and the maximum current peak value to obtain the voltage regulating resistance range, Indicates the maximum instantaneous rate of change of current flowing through the bidirectional thyristor; Step 4: Obtain the optimal values of component parameters by enumeration method with the maximum total energy on the resonant capacitor of the combined DC circuit breaker as the optimization target. 5. The method for designing parameters of a combined DC circuit breaker reclosing auxiliary device according to claim 4, characterized in that: Selection method of bidirectional thyristor in step 1: , Indicates the maximum instantaneous current change rate allowed when the bidirectional thyristor is turned on. 6. A combined DC circuit breaker reclosing auxiliary device and parameter design according to claim 5, characterized in that: Selection of voltage regulating resistors and protective inductors in steps 2 and 3: The resonant capacitor, voltage regulating resistor and protection inductor need to satisfy the following relationship: , In the formula, is the voltage regulating resistor, To protect the inductor, is the resonant capacitor. 7. A combined DC circuit breaker reclosing auxiliary device and parameter design according to claim 6, characterized in that: The enumeration method in step 4 uses steps 1, 2 and 3 as three constraints to obtain the minimum value of the protection inductor, the maximum value and the minimum value of the voltage regulating resistor. Based on the minimum value of the protection inductor, the maximum voltage on the resonant capacitor can be obtained by setting the step size.