Method for determining voltage and current during the converter valve shut-off process of anode saturated reactor

Abstract

The present invention relates to direct current transmission technology, and specifically to a method for determining the voltage and current during the turn-off process of a thyristor converter valve of an anode saturated reactor. The method comprises: simplifying the external circuit of the thyristor converter valve during the turn-off transient process; establishing a thyristor equivalent circuit during the turn-off transient process; establishing an equivalent model of the stored charge inside the thyristor during the turn-off process, taking into account the tolerance of the thyristor and setting different stored charges to obtain a thyristor equivalent model during the turn-off transient process; establishing an SR nonlinear model of the anode saturated reactor; obtaining the voltage and current magnitude of the thyristor converter valve at any moment during the turn-off process, as well as the voltage and current waveforms of the thyristor converter valve during the entire turn-off process. This method accurately analyzes the impact of the anode saturated reactor on the turn-off process; takes into account the different turn-off times caused by different stored charges due to the tolerance of the thyristor and the resulting impact, and can obtain the voltage across the thyristor and the current flowing through the thyristor at any point in the entire turn-off process.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current transmission, and in particular relates to a method for determining voltage and current during a switching-off process of a converter valve of an anode saturated reactor. Background Art

[0002] With the development of the economy and society and the growing demand for long-distance, high-capacity power transmission, HVDC transmission technology is increasingly being used in power systems. During the switching process, HVDC transmission thyristor valves experience sudden voltage fluctuations. Due to the presence of stray capacitance and inductance in the circuit, these sudden voltage fluctuations can further trigger voltage oscillations, generating transient voltage overshoots that can harm thyristors and other electrical components.

[0003] The anode saturation reactor is a key component in converter valve protection. In addition to limiting the current rise rate di / dt during thyristor turn-on, the current rapidly decreases during valve turn-off, causing the anode saturation reactor's core to become unsaturated, and its inductance gradually increases. The anode saturation reactor's voltage-dividing capability gradually increases, limiting the high voltage rise rate du / dt and suppressing the reverse peak voltage that could cause the valve to mis-turn on. Furthermore, the anode saturation reactor protects the thyristor by sharing the larger total valve voltage during overvoltage conditions.

[0004] In practical engineering applications, the current and voltage overshoots during the switching-off of thyristor valve commutation phases need to be strictly limited, which places demands on the parameter design of the anode saturated reactor. Therefore, it is necessary to accurately analyze the transient process of the commutation valve switching-off, taking into account the anode saturated reactor, and determine the voltage and current during the thyristor valve switching-off process to meet the design requirements. A previous method, "A Method for Determining the Voltage and Current During the Switch-off Process of a Converter Valve Including an Anode Saturated Reactor," simplified the turn-on process and determined the voltage and current during the thyristor valve commutation phase-on. However, the thyristor valve switching-off process differs significantly from the turn-on process, and the principle analysis and equivalent model of the turn-on process cannot be applied to the turn-off process. Therefore, it is necessary to analyze the thyristor valve switching-off process to determine the current and voltage during the thyristor valve switching-off process. However, no similar technical invention has yet been developed domestically or internationally. Summary of the Invention

[0005] In view of the problems existing in the background technology, the present invention provides a method for determining the voltage and current during the shutdown transient process of a DC transmission converter valve taking into account the anode saturation reactor.

[0006] To solve the above technical problems, the present invention adopts the following technical solution: a method for determining the voltage and current during the shut-off process of a converter valve of an anode saturated reactor, comprising the following steps:

[0007] Step 1: Use the A-phase DC voltage source, the B-phase DC voltage source, and the C-phase DC voltage source to replace the three-phase AC voltage source respectively, perform equivalent transformation on the capacitor branch, simplify the thyristor commutator valve that does not participate in the commutation process, and complete the simplification of the external circuit of the thyristor commutator valve during the transient shutdown process;

[0008] Step 2: For the thyristor commutator valve in the turn-off transient process, establish an equivalent circuit model of the thyristor commutator valve and simplify the damping branch to obtain a simplified thyristor equivalent circuit in the turn-off transient process;

[0009] An equivalent model of the stored charge inside the thyristor during the turn-off process is established. Taking into account the tolerance of the thyristor, different stored charges are set to obtain the equivalent model of the thyristor during the turn-off transient process.

[0010] Step 3: Establish the nonlinear model of the anode saturated reactor SR. The equivalent model of the anode saturated reactor includes the linear resistance R ek With linear inductance L mk , switch S srk Multiple branches formed by serial connection are connected in parallel, k is a positive integer;

[0011] Step 4: The voltage and current of the thyristor commutator valve at any moment during the shutdown process are obtained by simulating the experimental data, and the voltage and current waveforms of the thyristor commutator valve during the entire shutdown process are obtained by monitoring the oscilloscope.

[0012] In the above-mentioned method for determining the voltage and current during the converter valve closing process of the anode saturated reactor, the implementation of step 1 includes:

[0013] The simplified circuit of the external circuit during the thyristor valve turn-off transient process includes the A-phase DC voltage source U a , B phase DC voltage source U b , C-phase DC voltage source U c , A phase converter transformer leakage inductance, B phase converter transformer leakage inductance, C phase converter transformer leakage inductance, AB phase stray capacitance C ab , BC phase stray capacitance C bc , AC phase stray capacitance C ac , a first valve damping resistor, a first valve damping capacitor, a second valve damping resistor, a second valve damping capacitor and a thyristor commutation valve module T;

[0014] A-phase DC voltage source U a , B phase DC voltage source U b and C-phase DC voltage source U cOne end of the thyristor is connected together, and the other end is connected in series with one end of the leakage inductance of the A phase converter transformer, one end of the leakage inductance of the B phase converter transformer and one end of the leakage inductance of the C phase converter transformer. The first valve damping resistor is connected in series with the first valve damping capacitor to form an AB phase thyristor equivalent branch; the AB phase thyristor equivalent branch and the AB phase stray capacitance C ab After being connected in parallel, they are connected in series with the other end of the leakage inductance of the A-phase converter transformer and the leakage inductance of the B-phase converter transformer respectively; the second valve damping resistor and the second valve damping capacitor are connected in series to form an AC interphase thyristor equivalent branch; the AC interphase thyristor equivalent branch and the AC interphase stray capacitance C ac After parallel connection, they are connected in series with the other end of the leakage inductance of the A-phase converter transformer and the other end of the leakage inductance of the C-phase converter transformer respectively; the interphase stray capacitance C bc They are connected in series with the other end of the leakage inductance of the B phase converter transformer and the other end of the leakage inductance of the C phase converter transformer respectively; the thyristor converter valve module T and the BC phase stray capacitance C bc in parallel.

[0015] In the above-mentioned method for determining the voltage and current during the converter valve closing process of the anode saturated reactor, the implementation of step 2 includes:

[0016] Step 2.1, establish an equivalent circuit model of the thyristor valve during the turn-off transient process;

[0017] Step 2.1.1, the equivalent thyristor T v According to different charge storage conditions, it is divided into N i The thyristor group i includes the thyristor group i. gi , the i-th distributed capacitance C gi , the i-th damping resistor R dvi , the i-th damping capacitor C dvi , the i-th switch S tvi , i is a positive integer;

[0018] Step 2.1.2, the i-th distributed resistor R gi and the i-th distributed capacitance C gi In series, then connected to the i-th switch S tvi connected in parallel to form the equivalent branch of the i-th group of thyristors;

[0019] Step 2.1.3: Connect all thyristor equivalent branches in series to obtain the equivalent thyristor T v ; Connect all groups of damping resistors and damping capacitors in series to obtain the third valve damping resistor and the third valve damping capacitor;

[0020] Step 2.1.4, connect the third valve damping capacitor and the third valve damping resistor in series to form a valve damping branch; connect the valve damping branch to the thyristor T v Connect in parallel to form valve damping thyristor T vParallel branch; valve damping thyristor T v The parallel branch is connected in series with the anode saturated reactor SR to obtain the anode saturated reactor SR thyristor series branch; the anode saturated reactor SR thyristor series branch and the valve grading capacitor C j By connecting them in parallel, we can obtain the simplified thyristor equivalent circuit of the turn-off transient process;

[0021] Step 2.2: Establish an equivalent model of thyristor stored charge during the turn-off transient process:

[0022] Step 2.2.1, the equivalent model includes several voltage sources and corresponding number of damping resistors, and the distributed capacitance of the thyristor group 0 is C g0 ;

[0023] Step 2.2.2, set the i-th voltage source U tvn After being connected in series with the i-th damping resistor, a voltage source damping resistor series branch is formed; after all voltage source damping resistor series branches are connected in parallel, they are connected to the 0th group thyristor distributed capacitance C g0 Connect in parallel to form an equivalent circuit for storing charge;

[0024] Step 2.2.3, according to the stored charge of the i-th thyristor group, the voltage value of the voltage source is changed accordingly, thereby completing the corresponding stored charge setting;

[0025] Step 2.2.4: Monitor the direction of the current flowing through the series branch of the i-th voltage source and damping resistor, and control the i-th switch S in the i-th thyristor. tvi The working state of the thyristor is obtained, and the equivalent model of the turn-off transient process is obtained.

[0026] In the above-mentioned method for determining the voltage and current during the converter valve closing process of the anode saturated reactor, the implementation of step 3 includes:

[0027] Step 3.1, set up a plurality of linear resistor and linear inductor switch groups, wherein the i-th linear resistor and linear inductor switch group includes the i-th linear resistor (R ei ), the i-th linear inductance (L mi ) and the i-th switch (S sri ) in series; i is a positive integer;

[0028] Step 3.2: Connect all the linear resistor and linear inductor switch groups in parallel and control the i-th switch (S sri ) working state, and obtain the nonlinear model of the anode saturated reactor SR.

[0029] In the above-mentioned method for determining the voltage and current during the converter valve closing process of the anode saturated reactor, the leakage inductance of the A-phase converter transformer, the leakage inductance of the B-phase converter transformer, and the leakage inductance of the C-phase converter transformer are all L t , the first valve damping resistor and the third valve damping resistor are both Rdv , the first valve damping capacitor and the third valve damping capacitor are both C dv , the second valve damping resistor is R dv / 2, the second valve damping capacitance is 2C dv .

[0030] Compared with the prior art, the method for determining the voltage and current during the shutdown transient process of a DC transmission converter valve taking into account an anode saturated reactor provided by the present invention accurately analyzes the impact of the anode saturated reactor on the shutdown process; considers the differences in shutdown time caused by different stored charges due to thyristor tolerances and their resulting impact, analyzes the impact of the anode saturated reactor on the shutdown process, and performs precise modeling. This method can obtain the voltage and current values across the thyristor at any time point in the process, and can further obtain the waveforms of the voltage and current across the thyristor during the entire shutdown process. The obtained results are consistent with engineering practice and have guiding significance for the determination of parameters of various components of the converter valve and the design of the components. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A flowchart of a method for determining voltage and current during a shutdown process is provided for an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of the structure of the actual working circuit of the converter valve according to an embodiment of the present invention;

[0033] Among them, 1-first thyristor commutation valve, 2-second thyristor commutation valve, 3-third thyristor commutation valve, 4-fourth thyristor commutation valve, 5-fifth thyristor commutation valve, 6-sixth thyristor commutation valve;

[0034] Figure 3 This is a simplified topological diagram of the converter valve working circuit structure according to an embodiment of the present invention;

[0035] Figure 4 This is a topological diagram of an equivalent model of a thyristor in a turn-off transient process according to an embodiment of the present invention;

[0036] Figure 5 This is a topological diagram of an equivalent model of an anode saturated reactor according to an embodiment of the present invention;

[0037] FIG6( a ) is a current waveform diagram obtained according to an embodiment of the present invention;

[0038] FIG6( b ) is a voltage waveform diagram obtained according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0041] The present invention will be further described below with reference to specific examples, but they are not intended to limit the present invention.

[0042] With respect to the thyristor converter valve turn-off process, this embodiment provides a method for determining the voltage and current during the converter valve turn-off process including an anode saturated reactor. This method analyzes the influence of different components and system parameters on the voltage and current during the thyristor turn-off transient process, the influence of the stored charge inside the thyristor on the turn-off process, and the influence of different turn-off times caused by different stored charges on the turn-off process. The method particularly analyzes the influence of the anode saturated reactor to establish a mathematical model of the converter valve turn-off process taking into account the anode saturated reactor, build a circuit simulation model, and conduct simulation experiments based on the simulation model. By observing the waveforms shown on the oscilloscope, the accurate voltage and current during the thyristor converter valve turn-off transient process are obtained.

[0043] This embodiment is implemented by the following technical solution. The method for determining the voltage and current during the converter valve closing process of the anode saturated reactor includes the following steps:

[0044] (1) Three DC voltage sources are used to replace the three-phase AC voltage sources respectively, and the capacitor branch is transformed into an equivalent circuit. The thyristor commutator valve that does not participate in the commutation process is simplified, and the external circuit of the thyristor commutator valve during the transient shutdown process is simplified.

[0045] (2) For the thyristor commutator valve in the turn-off transient process, an equivalent circuit model of the thyristor commutator valve is established, and the damping branch is simplified to obtain the simplified thyristor equivalent circuit of the turn-off transient process; an equivalent model of the internal storage charge of the thyristor during the turn-off process is established, and considering the tolerance of the thyristor, different storage charges are set to obtain the thyristor equivalent model of the turn-off transient process;

[0046] (3) Establish the nonlinear model of the anode saturated reactor SR. The equivalent model of the anode saturated reactor consists of several linear resistors R ek With linear inductance L mk After parallel connection, the series switch S srk The branches formed are connected in parallel;

[0047] (4) The voltage and current of the thyristor commutator valve at any moment during the shutdown process are obtained through simulation experimental data, and the voltage and current waveforms of the thyristor commutator valve during the entire shutdown process are obtained by monitoring the oscilloscope.

[0048] Furthermore, the simplified circuit of the external circuit of the thyristor valve turning off transient process in step (1) includes a three-phase equivalent voltage source A phase DC voltage source U a , B phase DC voltage source U b , C-phase DC voltage source U c , A-phase converter transformer leakage inductance L t , B-phase converter transformer leakage inductance L t , C-phase converter transformer leakage inductance L t , stray capacitance C between AB phases ab , BC phase stray capacitance C bc , AC phase stray capacitance C ac , the first valve damping resistor R dv , the first valve damping capacitor C dv , the second valve damping resistor R dv / 2, the second valve damping capacitor 2C dv And thyristor commutation valve module T.

[0049] A-phase DC voltage source U a , B phase DC voltage source U b and C-phase DC voltage source U c One end is connected together, and the other end is connected to the leakage inductance L of the A phase converter transformer t , B-phase converter transformer leakage inductance L t and C-phase converter transformer leakage inductance L t connected in series to form the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch, second equivalent voltage source U b -B phase converter transformer leakage inductance L t Series branch, third equivalent voltage source U c -C phase converter transformer leakage inductance L t Series branch; first valve damping resistor R dv With the first valve damping capacitor C dv Connect in series to form an AB phase thyristor equivalent branch; the AB phase thyristor equivalent branch and the AB phase stray capacitance C ab After being connected in parallel, they are respectively connected to the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch, second equivalent voltage source U b -B phase converter transformer leakage inductance L t The series branches are connected in series; the first valve damping resistor R dvOne-half of the second valve damping resistance and the first valve damping capacitance C dv The second valve damping capacitor is connected in series with the AC phase thyristor equivalent branch, which is twice the AC phase stray capacitance C. ac After being connected in parallel, they are respectively connected to the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch and third equivalent voltage source U c -C phase converter transformer leakage inductance L t Series branches connected in series; BC interphase stray capacitance C bc and the second equivalent voltage source U b -B phase converter transformer leakage inductance L t Series branch and third equivalent voltage source U c -C phase converter transformer leakage inductance L t The series branches are connected in series; the thyristor valve module T and the BC interphase stray capacitance C bc By connecting them in parallel, the thyristor commutator valve turn-off transient process is obtained to simplify the external circuit.

[0050] Furthermore, in step (2), the simplified thyristor equivalent circuit of the turn-off transient process includes an anode saturation reactor SR, a third valve damping resistor R dv , the third valve damping capacitor C dv , valve equalizing capacitor C j , equivalent thyristor T v .

[0051] The thyristors are divided into several groups according to different charge storage conditions. The number of thyristors in group i is N. i The i-th distributed resistance is R gi , the i-th distributed capacitance is C gi , the i-th damping resistor is R dvi , the i-th damping capacitor is C dvi , the i-th switch is S tvi ; i is a positive integer.

[0052] The i-th distributed resistance R gi and the i-th distributed capacitance C gi After connecting in series, with the i-th switch S tvi Connect in parallel to form the i-th group of thyristor equivalent branches; connect all thyristor equivalent branches in series to obtain the equivalent thyristor T v ; Set the damping resistor R of all thyristor groups dvi With the damping capacitor C dvi Connect in series to obtain the third valve damping resistance R dv With the third valve damping capacitor C dv ;

[0053] The third valve damping capacitor Cdv And the valve equalizing capacitor C j Connected in series to form a valve damping branch; the valve damping branch and the equivalent thyristor T v Parallel connection to form valve damping - thyristor T v Parallel branch; connect the anode saturation reactor SR and the valve damping-thyristor T v The parallel branches are connected in series to obtain the anode saturation reactor SR-thyristor series branch; finally, the valve equalizing capacitor C j By connecting it in parallel with the anode saturation reactor S-thyristor series branch, the simplified turn-off transient process thyristor equivalent circuit is obtained.

[0054] Furthermore, the equivalent model of the thyristor during the turn-off transient process in step (2) is established. Several voltage sources are set, and the i-th voltage source is U tvi ; The equivalent model includes several voltage sources, the i-th damping resistor R s , the distributed capacitance of the thyristor group 0 C g0 ;

[0055] The i-th voltage source U tvi With the i-th damping resistor R s After connecting in series, a voltage source-damping resistor R is formed s Connect all voltage source-damping resistors R in series. s After the series branches are connected in parallel, the distributed capacitance C g0 Connected in parallel, they form an equivalent circuit for storing charge.

[0056] According to the charge storage of the i-th thyristor group, the i-th voltage source is changed to U tvi The voltage value of , thereby completing the corresponding storage charge setting;

[0057] Monitor the current flowing through the i-th voltage source-damping resistor R s The current direction of the series branch controls the i-th switch S in the i-th thyristor group tvi The working state of the thyristor is obtained, and the equivalent model of the turn-off transient process is obtained.

[0058] Furthermore, in step (3), several groups of linear resistors, linear inductors, and switches are set, and the linear resistor in the kth group is R ek , linear inductance is L mk , switch is S srk ;

[0059] The linear resistor R ek , linear inductance L mk With switch S srk connected in series to form a resistor R ek -Inductor L mk -Switch S srkConnect the branches in series to form a set of linear resistors, linear inductors and switches; connect all the linear resistors, linear inductors and switch groups in parallel to control the switch S srk The working state forms a nonlinear model of the anode saturated reactor SR.

[0060] In addition, in step (4), a simulation experiment is run to obtain simulation experiment data sorted by time, the time point to be observed is determined, and the voltage at both ends of the thyristor and the current flowing through the thyristor at the corresponding moment are obtained; the oscilloscope is turned on, and the oscilloscope waveform after the set turn-off moment is intercepted to obtain the voltage at both ends of the corresponding thyristor and the current flowing through the thyristor.

[0061] When implementing it specifically, Figure 1 As shown, the method for determining the voltage and current during the converter valve closing process of the anode saturated reactor includes the following steps:

[0062] First, three DC voltage sources are used to replace the three-phase AC voltage sources respectively, and the capacitor branch is equivalently transformed to simplify the thyristor commutator valve that does not participate in the commutation process, thus completing the simplification of the external circuit of the thyristor commutator valve during the transient shutdown process.

[0063] The structure of the actual working circuit of the converter valve is as follows Figure 2 As shown, during the commutation process, the voltage on the fifth thyristor commutator valve 5 drops to zero within a few microseconds and begins to conduct; while the current in the third thyristor commutator valve 3 decreases to zero and enters the off state.

[0064] Since the commutation time is very short, the instantaneous value of the three-phase voltage source does not change much, and the three-phase AC voltage source can be approximately replaced by a DC voltage source. In this embodiment, the time when the maximum shutdown overvoltage occurs is selected; Figure 2 The dotted line in the figure represents the current path from the third thyristor commutator valve 3 to the fifth thyristor commutator valve 5, while the thick solid line represents the current path conducted through the third thyristor commutator valve 3 and the fourth thyristor commutator valve 4; the distributed transformer and switch station capacitance are represented by lumped elements C t and C y It means that all capacitors can be equivalent to the stray capacitance C between AB phases through capacitance transformation. ab , BC phase stray capacitance C bc , AC phase stray capacitance C ac .

[0065] Since the research object is the thyristor commutator valve that changes from the on state to the off state, the thyristor commutator valve that remains in the on state or the off state during the process can be treated equivalently: for the thyristor commutator valve in the off state, since the distributed resistance of the thyristor is large and the distributed capacitance is small, it can be ignored. The thyristor commutator valve in the off state is treated as a valve damping resistor R dv and valve damping capacitor Cdv Indicates that; for the thyristor commutator valve in the open state, since the thyristor conduction resistance is very small, it can be regarded as a short circuit; then the equivalent model of the thyristor commutator valve with unchanged state is simplified by series and parallel calculation, and the following can be obtained: Figure 3 The simplified converter valve working circuit is shown.

[0066] The simplified converter valve working circuit includes three-phase equivalent voltage sources: A-phase DC voltage source U a , B phase DC voltage source U b and C-phase DC voltage source U c , converter transformer leakage inductance L t , stray capacitance C between AB phases ab , BC phase stray capacitance C bc , AC phase stray capacitance C ac , valve damping resistance R dv , valve damping capacitance C dv and a thyristor commutation valve module T;

[0067] A-phase DC voltage source U a , B phase DC voltage source U b and C-phase DC voltage source U c One end is connected together, and the other end is connected to the leakage inductance L of the A phase converter transformer t , B-phase converter transformer leakage inductance L t and C-phase converter transformer leakage inductance L t connected in series to form the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch, second equivalent voltage source U b -B phase converter transformer leakage inductance L t Series branch, third equivalent voltage source U c -C phase converter transformer leakage inductance L t Series branch; first valve damping resistor R dv With the first valve damping capacitor C dv Connect in series to form an AB phase thyristor equivalent branch; the AB phase thyristor equivalent branch and the AB phase stray capacitance C ab After being connected in parallel, they are respectively connected to the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch, second equivalent voltage source U b -B phase converter transformer leakage inductance L t The series branches are connected in series; the first valve damping resistor R dv One-half of the second valve damping resistance and the first valve damping capacitance C dvThe second valve damping capacitor is connected in series with the AC phase thyristor equivalent branch, which is twice the AC phase stray capacitance C. ac After being connected in parallel, they are respectively connected to the first equivalent voltage source U a -A phase converter transformer leakage inductance L t Series branch and third equivalent voltage source U c -C phase converter transformer leakage inductance L t Series branches connected in series; BC interphase stray capacitance C bc and the second equivalent voltage source U b -B phase converter transformer leakage inductance L t Series branch and third equivalent voltage source U c -C phase converter transformer leakage inductance L t The series branches are connected in series; the thyristor valve module T and the BC interphase stray capacitance C bc By connecting them in parallel, the thyristor commutator valve turn-off transient process is obtained to simplify the external circuit.

[0068] 2. For the thyristor commutator valve in the shutdown transient process, an equivalent circuit model of the thyristor commutator valve is established, and the damping branch is simplified to obtain the simplified thyristor equivalent circuit of the shutdown transient process; an equivalent model of the internal stored charge of the thyristor during the shutdown process is established, and considering the tolerance of the thyristor, different stored charges are set to obtain the thyristor equivalent model of the shutdown transient process.

[0069] The thyristors of the third thyristor commutator valve 3 contain non-neutral carriers, which can be represented by stored charge. This stored charge will cause the third thyristor commutator valve 3 to conduct in the reverse direction, manifested as: the current flowing through the third thyristor commutator valve 3 is opposite to the current when it is conducting, but the voltage across the third thyristor commutator valve 3 remains zero. Due to the tolerances of different thyristors, the stored charge values of each thyristor are not equal. The thyristors of the third thyristor commutator valve 3 will be turned off in sequence, increasing the impedance presented to the valve at a finite rate, and eventually tending to stabilize.

[0070] To simplify the model while ensuring accuracy, thyristors with similar stored charge can be grouped into one group, and thyristors can be divided into several groups according to different stored charge amounts. If the distributed resistance of a single thyristor is R g , the distributed capacitance is C g , for N i The equivalent distributed resistance R gi and the equivalent partial capacitance C gi They are:

[0071]

[0072] The number of thyristor groups should be selected in combination with the actual project situation and the complexity of simulation modeling, and the simulation operation should be simplified while ensuring accuracy. Based on the above considerations, this embodiment selects 7 groups of thyristors, such as Figure 4 shown.

[0073] The thyristors are divided into groups i (i=0, 1…6) according to different charge storage conditions. The larger i is, the greater the amount of charge stored by the thyristors in the group. The number of thyristors in the i-th group is N i The distributed resistance is R gi , the distributed capacitance is C gi , the damping resistor is R dvi , the damping capacitor is C dvi , the switch included is S tvi .

[0074] Distributed resistance R gi and distributed capacitance C gi After connecting in series, with switch S tvi Connect in parallel to form the i-th group of thyristor equivalent branches; connect all thyristor equivalent branches in series to obtain the equivalent thyristor T v ; Set the damping resistor R of all thyristor groups dvi With the damping capacitor C dvi Connect in series to obtain the valve damping resistance R dv and valve damping capacitor C dv ;

[0075] Valve damping capacitor C dv And the valve equalizing capacitor C j Connected in series to form a valve damping branch; the valve damping branch and the thyristor T v Parallel connection to form valve damping - thyristor T v Parallel branch; connect the anode saturation reactor SR and the valve damping-thyristor module T v The parallel branches are connected in series to obtain the anode saturation reactor SR-thyristor series branch; finally, the valve equalizing capacitor C j By connecting it in parallel with the anode saturation reactor SR-thyristor series branch, the simplified thyristor equivalent circuit of the turn-off transient process is obtained.

[0076] The charge stored in a capacitor satisfies the relationship between the capacitance and the charge stored in the capacitor:

[0077]

[0078] Where C represents the capacitance of the capacitor, ΔQ represents the change in the charge stored in the capacitor, and U represents the change in the voltage across the capacitor. Therefore, the change in the charge stored in the capacitor can be determined by the change in the voltage across the capacitor. According to the stored charge of the thyristor in the i-th group, the corresponding voltage source is set. The i-th group corresponds to the voltage source U. tvi; Among them, group 0 has no corresponding voltage source; when the stored charge of group 0 thyristors is completely released, the distributed capacitance C of group 0 thyristors g0 The voltage across the two ends is 0; the stored charge continues to be released, which will cause the capacitor C g0 The voltage across both ends increases.

[0079] Therefore, the voltage source U tvi (i=1,2…6) and damping resistor R s After connecting in series, a voltage source-damping resistor R is formed s Connect all voltage sources - damping resistors R in series. s After the series branches are connected in parallel, the distributed capacitance C g0 In parallel, a charge storage equivalent circuit is formed; according to the charge storage situation of the i-th thyristor group, the voltage source U is changed accordingly tvi The voltage value is set to complete the corresponding storage charge setting;

[0080] Monitor the current flowing through the i-th voltage source—damping resistor R s The current direction of the series branch, when the current direction changes, it means that the stored charge on the distributed capacitance of the i-th group of thyristors is completely released and enters the off state. At this time, the control circuit can be used to control the switch S in the i-th thyristor group. i The turn-off transient process of the thyristor is obtained.

[0081] 3. Establish the nonlinear model of anode saturated reactor SR. The equivalent model of anode saturated reactor consists of several linear resistors R ei With linear inductance L mi After parallel connection, the series switch S sri The branches formed are connected in parallel.

[0082] In the initial stage of thyristor turn-off, the current flowing through the anode saturated reactor is very large, manifesting as a relatively small inductance. As the turn-off current decreases, the anode saturated reactor gradually enters an unsaturated state, and the inductance value increases, exhibiting a distinct nonlinear UI characteristic. This embodiment controls the on-off states of several linear resistor-linear inductor-switch groups to present the nonlinear external characteristics of the anode saturated reactor SR and establish a nonlinear equivalent model of the anode saturated reactor. The resistance and inductance values of each linear resistor-linear inductor-switch group can be determined based on the actual external characteristics of the anode saturated reactor.

[0083] The number of groups should be selected in combination with the actual project situation and the complexity of simulation modeling, and the simulation operation should be simplified while ensuring accuracy. Based on the above considerations, this embodiment selects 5 groups of linear resistors, linear inductors, and switches, such as Figure 5 shown.

[0084] The linear resistor Rei , linear inductance L mi With switch S sri (i=1,2…5) are connected in series to form a resistor R ei -Inductor L mi -Switch S sri Connect the branches in series to form a set of linear resistors, linear inductors and switches; connect all the linear resistors, linear inductors and switch groups in parallel to control the switch S sri The working state forms a nonlinear model of the anode saturated reactor SR.

[0085] 4. Through the simulation experimental data, the voltage and current of the thyristor commutator valve at any time during the shutdown process are obtained, and by monitoring the oscilloscope, the current waveform and current waveform of the thyristor commutator valve during the full shutdown process are obtained, as shown in Figure 6(a) and Figure 6(b).

[0086] based on Figure 2 、 Figure 3 、 Figure 4 Build a simulation model based on the circuit model shown, run the simulation experiment, obtain simulation experiment data sorted by time, determine the time point that needs to be observed, and obtain the voltage across the thyristor and the current flowing through the thyristor at the corresponding moment; turn on the oscilloscope, intercept the oscilloscope waveform after the set turn-off moment, and obtain the voltage across the thyristor and the current flowing through the thyristor.

[0087] The present invention provides a method for determining the voltage and current during the transient shutdown process of a DC transmission converter valve considering an anode saturated reactor. The method analyzes the transient shutdown process of the converter valve, considers the differences in shutdown time caused by different stored charges due to tolerances of thyristors and their resulting impact, and particularly analyzes the impact of the anode saturated reactor on the shutdown process. A mathematical model of the converter valve shutdown process considering the anode saturated reactor is established, a circuit simulation model is constructed, and simulation experiments are performed based on the simulation model to obtain the voltage and current values across the thyristor at any time point in the process, and can further obtain the waveforms of the voltage and current across the thyristor during the entire shutdown process.

[0088] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the present invention specification should be included in the protection scope of the present invention.

Claims

1. A method for determining the voltage and current during the closing process of a converter valve of an anode saturated reactor, characterized by: The following steps are involved: Step 1: Use the A-phase DC voltage source, the B-phase DC voltage source, and the C-phase DC voltage source to replace the three-phase AC voltage source respectively, perform equivalent transformation on the capacitor branch, simplify the thyristor commutator valve that does not participate in the commutation process, and complete the simplification of the external circuit of the thyristor commutator valve during the transient shutdown process; the implementation method is as follows: The simplified circuit of the external circuit during the thyristor valve turn-off transient process includes a phase A DC voltage source ( U a )、B-phase DC voltage source( U b )、C-phase DC voltage source( U c ), A-phase converter transformer leakage inductance, B-phase converter transformer leakage inductance, C-phase converter transformer leakage inductance, AB phase stray capacitance ( C ab ), BC phase stray capacitance ( C bc )、AC interphase stray capacitance( C ac ), the first valve damping resistor, the first valve damping capacitor, the second valve damping resistor, the second valve damping capacitor and the thyristor commutation valve module ( T ); A-phase DC voltage source ( U a )、B-phase DC voltage source( U b ) and C-phase DC voltage source ( U c ) are connected together, and the other ends are connected in series with one end of the leakage inductance of the A-phase converter transformer, one end of the leakage inductance of the B-phase converter transformer, and one end of the leakage inductance of the C-phase converter transformer. The first valve damping resistor is connected in series with the first valve damping capacitor to form an AB phase thyristor equivalent branch; the AB phase thyristor equivalent branch and the AB phase stray capacitance ( C ab ) are connected in parallel and are connected in series with the other ends of the leakage inductance of the A-phase converter transformer and the B-phase converter transformer respectively; the second valve damping resistor and the second valve damping capacitor are connected in series to form an AC interphase thyristor equivalent branch; the AC interphase thyristor equivalent branch and the AC interphase stray capacitance ( C ac ) are connected in parallel and then connected in series with the other end of the leakage inductance of the A-phase converter transformer and the other end of the leakage inductance of the C-phase converter transformer; the interphase stray capacitance of BC ( C bc ) are connected in series with the other end of the leakage inductance of the B-phase converter transformer and the other end of the leakage inductance of the C-phase converter transformer; the thyristor converter valve module ( T ) and BC interphase stray capacitance ( C bc )in parallel; Step 2: For the thyristor commutator valve in the turn-off transient process, establish an equivalent circuit model of the thyristor commutator valve and simplify the damping branch to obtain a simplified thyristor equivalent circuit of the turn-off transient process; including the following steps: Step 2.1, establish an equivalent circuit model of the thyristor valve during the turn-off transient process; Step 2.1.1, the equivalent thyristor ( T v ) According to different charge storage conditions, it is divided into N i group of thyristors, among which the i The thyristor group includes i Distributed resistance ( R gi ), No. i Distributed capacitance ( C gi ), No. i Damping resistor ( R dvi ), No. i Damping capacitor ( C dvi ), No. i switch( S tvi ), i is a positive integer; Step 2.1.2, i Distributed resistance ( R gi ) and i Distributed capacitance ( C gi ) in series, and then connected to the i switch( S tvi ) in parallel to form the i Group thyristor equivalent branch; Step 2.1.3, connect all the thyristor equivalent branches in series to obtain the equivalent thyristor ( T v ); Connect all groups of damping resistors and damping capacitors in series to obtain the third valve damping resistor and the third valve damping capacitor; Step 2.1.4, connect the third valve damping capacitor and the third valve damping resistor in series to form a valve damping branch; connect the valve damping branch to the thyristor ( T v ) in parallel to form a valve damping thyristor ( T v ) parallel branch; valve damping thyristor ( T v ) parallel branch and anode saturation reactor ( SR ) in series, we get the anode saturation reactor ( SR ) thyristor series branch; anode saturation reactor ( SR ) thyristor series branch and valve equalizing capacitor ( C j ) are connected in parallel to obtain the simplified thyristor equivalent circuit of the turn-off transient process; Step 2.2: Establish an equivalent model of thyristor stored charge during the turn-off transient process: Step 2.2.1, the equivalent model includes several voltage sources and corresponding number of damping resistors, as well as the distributed capacitance of the thyristor group 0 ( C g0 ); Step 2.2.2, i A voltage source ( U tvn ) and i After the damping resistors are connected in series, a voltage source damping resistor series branch is formed; after all the voltage source damping resistor series branches are connected in parallel, together with the 0th group of thyristor distributed capacitance ( C g0 ) are connected in parallel to form an equivalent circuit for storing charge; Step 2.2.3, according to i The stored charge situation of each thyristor group is adjusted accordingly to change the voltage value of the voltage source, thereby completing the corresponding stored charge setting; Step 2.2.4, monitor the flow through i The direction of the current in the voltage source damping resistor series branch controls the i Thyristor i switch( S tvi ) working state, and obtain the thyristor equivalent model of the turn-off transient process; Step 3: Build anode saturation reactor SR Nonlinear model, the equivalent model of anode saturated reactor includes linear resistance ( R ek ) and linear inductance ( L mk ),switch( S srk ) are connected in series to form multiple branches in parallel. k is a positive integer; Step 4: The voltage and current of the thyristor commutator valve at any moment during the shutdown process are obtained by simulating the experimental data, and the voltage and current waveforms of the thyristor commutator valve during the entire shutdown process are obtained by monitoring the oscilloscope.

2. The method for determining the voltage and current during the converter valve shut-off process of the anode saturated reactor according to claim 1, characterized in that: The implementation of step 3 includes: Step 3.1, set up several groups of linear resistor and linear inductor switch groups, among which the first i The linear resistor and linear inductor switch group includes the i Linear resistance ( R ei ), No. i Linear inductance ( L mi ) and i switch( S sri ) in series; i 1, 2, 3..., k ; Step 3.2, connect all the linear resistor and linear inductor switch groups in parallel and control the i switch( S sri ) working state, and obtain the anode saturation reactor ( SR ) nonlinear model.

3. The method for determining the voltage and current during the converter valve closing process of the anode saturated reactor according to claim 1, characterized in that: The leakage inductance of the A-phase converter transformer, the B-phase converter transformer and the C-phase converter transformer are all L t , the first valve damping resistor and the third valve damping resistor are both R dv , the first valve damping capacitor and the third valve damping capacitor are both C dv , the second valve damping resistance is R dv / 2, the second valve damping capacitance is 2 C dv .

Images