阅读说明：本技术 一种高压直流输电混合换流器的控制方法 (Control method of high-voltage direct-current transmission hybrid converter ) 是由 曾嵘 许超群 张翔宇 余占清 赵彪 陈政宇 于 2020-03-31 设计创作，主要内容包括：本发明提供一种高压直流输电混合换流器的控制方法,包括：分析采用所述混合换流器的系统的物理特征,对所述物理特征进行评价,判断所述混合换流器处于下面哪一种状态：换相失败、换相失败概率高、换相失败概率不高,如果所述混合换流器处于换相失败的状态,关断所述混合换流器的被换相桥臂,从而强制换相；如果所述混合换流器处于换相失败概率高的状态,提前使所述混合换流器的被换相桥臂保持关断,从而强制换相；如果所述混合换流器处于换相失败概率不高的状态,维持所述混合换流器的运行。本发明提高了所述高压直流输电混合换流器的抵御换相失败能力,减少了换相失败故障发生次数。(The invention provides a control method of a high-voltage direct-current transmission hybrid converter, which comprises the following steps: analyzing the physical characteristics of the system adopting the hybrid converter, evaluating the physical characteristics, and judging which of the following states the hybrid converter is in: if the hybrid converter is in a phase commutation failure state, switching off a phase commutated bridge arm of the hybrid converter so as to forcibly commutate; if the hybrid converter is in a state with high probability of commutation failure, keeping a commutated bridge arm of the hybrid converter to be turned off in advance, and thus forcibly commutating the phase; and if the hybrid converter is in a state with low probability of commutation failure, maintaining the operation of the hybrid converter. The invention improves the capability of resisting commutation failure of the high-voltage direct-current transmission hybrid converter and reduces the frequency of commutation failure faults.)

1. A control method of a high-voltage direct-current transmission hybrid converter is characterized by comprising the following steps:

analyzing physical characteristics of a system adopting the high-voltage direct-current transmission hybrid converter, evaluating the physical characteristics, and judging which state the high-voltage direct-current transmission hybrid converter is in: commutation failure, high probability of commutation failure, low probability of commutation failure,

if the high-voltage direct-current transmission hybrid converter is in a phase change failure state, a phase-changed bridge arm of the high-voltage direct-current transmission hybrid converter is turned off, so that the phase is forcibly changed;

and if the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability, keeping a commutated bridge arm of the high-voltage direct-current transmission hybrid converter switched off in advance, and thus forcibly commutating.

And if the high-voltage direct-current transmission hybrid converter is in a state of low probability of commutation failure, maintaining the operation of the high-voltage direct-current transmission hybrid converter.

2. A method of controlling a HVDC hybrid converter according to claim 1,

the physical characteristics include:

the inversion side of the system has three-phase alternating voltage and three-phase alternating current,

the dc side dc current and dc voltage of the system,

bridge arm current, bridge arm voltage and turn-off angle of the high-voltage direct-current transmission hybrid converter.

3. A method of controlling a HVDC hybrid converter according to claim 2,

if any bridge arm current or bridge arm voltage of the high-voltage direct-current transmission hybrid converter undergoes reduction to 0, but within a cycle, the bridge arm current or the bridge arm voltage is reestablished and increased to a rated value, or

The bridge arm current or bridge arm voltage experiences a drop in a cycle and then rises again to the target value, or

The change rate of the bridge arm current or the bridge arm voltage has a process that the change rate is less than 0, equal to 0 and greater than 0 in sequence in a cycle,

and judging that the high-voltage direct-current transmission hybrid converter is in the state of phase commutation failure.

4. A method of controlling a HVDC hybrid converter according to claim 2,

and if the system judges that the turn-off angle is smaller than the inherent turn-off angle of the hybrid converter in the phase commutation process, judging that the high-voltage direct-current transmission hybrid converter is in the state of failed phase commutation.

5. A method of controlling a HVDC hybrid converter according to claim 2,

and if the bridge arm voltage goes through a process of changing from negative to positive and dropping to 0 before the forward bridge arm voltage is not established to a rated value, determining that the high-voltage direct-current transmission hybrid converter is in a phase change failure state.

6. A method of controlling a HVDC hybrid converter according to claim 2,

when the minimum dropping amplitude of the three-phase alternating voltage or the three-phase alternating current is not lower than 40%, judging that the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability;

and when the maximum dropping amplitude of the three-phase alternating-current voltage or the three-phase alternating-current is lower than 40%, determining that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

7. A method of controlling a HVDC hybrid converter according to claim 2,

further comprising the step of A:

when the commutation area of the three-phase alternating voltage or the three-phase alternating current is not more than 70% of the minimum commutation area of the three-phase alternating voltage or the three-phase alternating current when the system successfully commutates, determining that the high-voltage direct-current transmission hybrid converter is in a state with high probability of commutation failure;

and when the commutation area of the three-phase alternating voltage or the three-phase alternating current is larger than 70% of the minimum commutation area of the three-phase alternating voltage or the three-phase alternating current when the system successfully commutates, determining that the high-voltage direct-current power transmission hybrid converter is in a state with low probability of commutation failure.

8. A method of controlling a HVDC hybrid converter according to claim 7,

before the step A, the three-phase alternating voltage and the three-phase alternating current are continuously sampled for a plurality of times, and sin-cos decomposition detection is carried out on the sampled data, so that the commutation area of the three-phase alternating voltage and the three-phase alternating current is calculated.

9. A method of controlling a HVDC hybrid converter according to claim 2,

carrying out harmonic decomposition on the direct current voltage and the direct current voltage, extracting harmonic characteristics for analysis, then carrying out commutation area calculation on each obtained harmonic,

when the sum of the area coefficients of the commutation of each subharmonic is not less than 10%, determining that the high-voltage direct-current transmission hybrid converter is in a state with high probability of commutation failure;

and when the sum of the area coefficients of the commutation of each subharmonic is lower than 10%, determining that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

10. A method of controlling a HVDC hybrid converter according to claim 2,

when the bridge arm current is higher than the maximum turn-off current, the high-voltage direct-current transmission hybrid converter is judged to be in a state with high commutation failure probability;

and when the bridge arm current is not higher than the maximum turn-off current, judging that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

11. A method of controlling a HVDC hybrid converter according to any one of claims 3 to 5,

and if the high-voltage direct-current transmission hybrid converter is in the state of failed commutation, a converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-commutated bridge arm of the high-voltage direct-current transmission hybrid converter.

12. A method of controlling a HVDC hybrid converter according to any one of claims 6 to 10,

if the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability, a converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-shifted bridge arm of the high-voltage direct-current transmission hybrid converter;

and if the high-voltage direct-current transmission hybrid converter is in a state that the probability of commutation failure is not high, keeping the operation mode of the high-voltage direct-current transmission hybrid converter unchanged.

Technical Field

The invention belongs to the field of direct current transmission, and particularly relates to a control method of a high-voltage direct current transmission hybrid converter.

Background

The existing High-Voltage Direct Current (HVDC) transmission technology is widely applied at present due to the advantages of large transmission capacity, low loss, High reliability and the like. And the failure of commutation is one of the faults with higher occurrence probability of the direct current transmission system. In the converter, the valve which is out of conduction can not restore the blocking capability within a period of time when the reverse voltage acts, or the phase change process is not completed during the reverse voltage, when the valve voltage changes to the positive direction, the phase of the valve which is out of conduction is changed to the original valve which is out of conduction, and the condition is called phase change failure. A failure in commutation will cause the converter valves to latch up, interrupting the transmission channels of the dc system, and in severe cases may cause a grid collapse.

The traditional high-voltage direct-current transmission converter adopts a three-phase bridge type rectifying unit formed by thyristors as a basic unit, wherein each bridge arm is formed by a thyristor valve string, but the thyristor valve string can not actively control current to be turned off, so that the traditional high-voltage direct-current transmission converter has larger current conversion current and reactive support, the risk of phase conversion failure exists, and the reliability needs to be improved.

Disclosure of Invention

In order to solve the problems, the invention provides a control method of a high-voltage direct-current transmission hybrid converter for resisting commutation failure.

The invention provides a control method of a high-voltage direct-current transmission hybrid converter, which comprises the following steps:

analyzing physical characteristics of a system adopting the high-voltage direct-current transmission hybrid converter, evaluating the physical characteristics, and judging which state the high-voltage direct-current transmission hybrid converter is in: commutation failure, high probability of commutation failure, low probability of commutation failure,

if the high-voltage direct-current transmission hybrid converter is in a phase change failure state, a phase-changed bridge arm of the high-voltage direct-current transmission hybrid converter is turned off, so that the phase is forcibly changed;

and if the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability, keeping a commutated bridge arm of the high-voltage direct-current transmission hybrid converter switched off in advance, and thus forcibly commutating.

And if the high-voltage direct-current transmission hybrid converter is in a state of low probability of commutation failure, maintaining the operation of the high-voltage direct-current transmission hybrid converter.

Further, in the present invention,

the physical characteristics include:

the inversion side of the system has three-phase alternating voltage and three-phase alternating current,

the dc side dc current and dc voltage of the system,

bridge arm current, bridge arm voltage and turn-off angle of the high-voltage direct-current transmission hybrid converter.

Further, in the present invention,

if any bridge arm current or bridge arm voltage of the high-voltage direct-current transmission hybrid converter undergoes reduction to 0, but within a cycle, the bridge arm current or the bridge arm voltage is reestablished and increased to a rated value, or

The bridge arm current or bridge arm voltage experiences a drop in a cycle and then rises again to the target value, or

The change rate of the bridge arm current or the bridge arm voltage has a process that the change rate is less than 0, equal to 0 and greater than 0 in sequence in a cycle,

and judging that the high-voltage direct-current transmission hybrid converter is in the state of phase commutation failure.

Further, in the present invention,

and if the system judges that the turn-off angle is smaller than the inherent turn-off angle of the hybrid converter in the phase commutation process, judging that the high-voltage direct-current transmission hybrid converter is in the state of failed phase commutation.

Further, in the present invention,

and if the bridge arm voltage goes through a process of changing from negative to positive and dropping to 0 before the forward bridge arm voltage is not established to a rated value, determining that the high-voltage direct-current transmission hybrid converter is in a phase change failure state.

Further, in the present invention,

when the minimum dropping amplitude of the three-phase alternating voltage or the three-phase alternating current is not lower than 40%, judging that the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability;

and when the maximum dropping amplitude of the three-phase alternating-current voltage or the three-phase alternating-current is lower than 40%, determining that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

Further, in the present invention,

further comprising the step of A:

when the commutation area of the three-phase alternating voltage or the three-phase alternating current is not more than 70% of the minimum commutation area of the three-phase alternating voltage or the three-phase alternating current when the system successfully commutates, determining that the high-voltage direct-current transmission hybrid converter is in a state with high probability of commutation failure;

and when the commutation area of the three-phase alternating voltage or the three-phase alternating current is larger than 70% of the minimum commutation area of the three-phase alternating voltage or the three-phase alternating current when the system successfully commutates, determining that the high-voltage direct-current power transmission hybrid converter is in a state with low probability of commutation failure.

Further, in the present invention,

before the step A, the three-phase alternating voltage and the three-phase alternating current are continuously sampled for a plurality of times, and sin-cos decomposition detection is carried out on the sampled data, so that the commutation area of the three-phase alternating voltage and the three-phase alternating current is calculated.

Further, in the present invention,

carrying out harmonic decomposition on the direct current voltage and the direct current voltage, extracting harmonic characteristics for analysis, then carrying out commutation area calculation on each obtained harmonic,

when the sum of the area coefficients of the commutation of each subharmonic is not less than 10%, determining that the high-voltage direct-current transmission hybrid converter is in a state with high probability of commutation failure;

and when the sum of the area coefficients of the commutation of each subharmonic is lower than 10%, determining that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

Further, in the present invention,

when the bridge arm current is higher than the maximum turn-off current, the high-voltage direct-current transmission hybrid converter is judged to be in a state with high commutation failure probability;

and when the bridge arm current is not higher than the maximum turn-off current, judging that the high-voltage direct-current transmission hybrid converter is in a state with low probability of commutation failure.

Further, in the present invention,

and if the high-voltage direct-current transmission hybrid converter is in the state of failed commutation, a converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-commutated bridge arm of the high-voltage direct-current transmission hybrid converter.

Further, in the present invention,

if the high-voltage direct-current transmission hybrid converter is in a state with high commutation failure probability, a converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-shifted bridge arm of the high-voltage direct-current transmission hybrid converter;

and if the high-voltage direct-current transmission hybrid converter is in a state that the probability of commutation failure is not high, keeping the operation mode of the high-voltage direct-current transmission hybrid converter unchanged.

The invention relates to a control method of a high-voltage direct-current transmission hybrid converter, which aims at the problem of the existing high-voltage direct-current transmission converter that the phase commutation fails, adopts a novel high-voltage direct-current transmission hybrid converter and utilizes a converter control method of rapid phase commutation failure detection and identification, and improves the capability of the converter for resisting the phase commutation failure, thereby reducing the frequency of the phase commutation failure.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 shows a schematic diagram of a high voltage dc transmission hybrid converter using the control method of the present invention;

fig. 2 shows a control logic diagram of a control method of a high voltage direct current transmission hybrid converter according to an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Fig. 1 shows a structure of a high-voltage dc transmission hybrid converter using the control method of the present invention. As can be seen from fig. 1, the high-voltage dc transmission hybrid converter has 6 identical legs: ap, An, Bp, Bn, Cp, Cn; and points P and N are direct-current voltage connection points respectively, points P are positive electrodes, points N are negative electrodes, and points A, B and points C are connection points of the high-voltage direct-current transmission hybrid converter and three-phase alternating current.

Wherein the content of the first and second substances,

each bridge arm is composed of a thyristor valve string and a turn-off thyristor valve string, and each thyristor valve string is composed of k thyristors (S)₁～S_k) Is composed of m disconnectable tubes (Q) connected in series, k is an integer greater than or equal to 1, and each disconnectable tube valve string is composed of m disconnectable tubes (Q)₁……Q_m) The components are connected in series, and m is an integer more than or equal to 1; in each thyristor valve string, the anode of the previous thyristor is connected with the cathode of the next thyristor to realize series connection; the connection point of the thyristor valve string and the turn-off pipe valve string is T; the thyristor is a unidirectional thyristor, and the pipe valve string capable of being turned off can comprise one or more of IGCT or GTO with reverse blocking capability or IGBT modified turn-off device (series connection), or IGCT or GTO without reverse blocking capability or IGBT turn-off device and diode series connection combination, or IEGT (enhanced gate transistor), GTR (power transistor), MOSFET (power field effect transistor) without reverse blocking capability and diode series connection combination.

Of the three first legs Ap, Bp and Cp of said legs, the thyristor S of the first end of the thyristor valve string₁The cathode of the thyristor is connected to the positive pole P of the direct voltage, and the thyristor S at the second end of the thyristor valve string_kIs connected to the connecting point T of the thyristor valve string and the turn-off pipe valve string;

in the three second arms An, Bn and Cn of the arms, the thyristor S at the first end of the thyristor valve string₁The cathodes of the thyristors in the series are connected to the three-phase AC connection points A, B and C, and the thyristors S at the second end of the series are connected to_kIs connected to the junction T of the thyristor valve string and the closable pipe valve string.

Since there may be uncertain disturbances generated when the hvdc transmission hybrid converter is in normal operation, the disturbances will possibly cause distortion of physical characteristics of the hvdc transmission hybrid converter, eventually causing a phase commutation failure. Aiming at the problem of phase commutation failure, the invention provides a control method for resisting the phase commutation failure for the high-voltage direct-current transmission hybrid converter. The control method of the invention mainly aims to realize the purpose of resisting commutation failure finally through rapid commutation failure prediction, detection, commutation failure identification and corresponding control.

Referring to fig. 2, specifically, the control method of the high voltage direct current transmission hybrid converter of the present invention includes the steps of:

1) with the occurrence of disturbance, analyzing relevant physical characteristics or electrical characteristics of a system adopting the high-voltage direct-current transmission hybrid converter, namely detecting the amplitude and the change rate of electrical quantities such as three-phase alternating-current voltage and three-phase alternating-current at an inversion side, direct-current and direct-current voltage at a direct-current side, current and voltage of each bridge arm of the high-voltage direct-current transmission hybrid converter, and the like through the system, extracting and comparing the characteristics of the electrical quantities with corresponding electrical quantities in normal operation, and comprehensively evaluating or considering according to waveform characteristics: if the phase change process of the high-voltage direct-current transmission hybrid converter is that the current of an original bridge arm is transferred to a phase change bridge arm, if the current or the voltage of a certain bridge arm is reduced to 0, but in a cycle, the current or the voltage is reestablished and increased to a rated value, or the current or the voltage of a certain bridge arm is reduced in a cycle and then immediately increased to the rated value, namely, the change rate of the current or the voltage of the bridge arm is a process of sequentially reducing to <0, <0 and >0 in a cycle, the phase change failure at the moment can be judged. If the bridge arm voltage goes through a process of changing from negative to positive, but the forward bridge arm voltage drops to 0 before the rated value is not established, it can be judged that phase commutation failure has occurred at the moment. Or in the whole operation process of the hybrid converter, a turn-off angle control link in a control system judges, and if the turn-off angle of the current commutation is smaller than the inherent turn-off angle of the hybrid converter, the commutation failure can be confirmed to occur at the moment.

According to the existing data statistics, the invention judges that the commutation failure probability reaches more than 70% when the minimum dropping amplitude of the three-phase alternating-current voltage or the three-phase alternating-current is more than 40%, so that the invention takes the situation that the commutation failure probability is high when the minimum dropping amplitude of the three-phase alternating-current voltage or the three-phase alternating-current is not less than 40%, namely the commutation failure occurrence probability is not less than 70%; when the maximum drop width of the three-phase ac voltage or the three-phase ac current is 40% or less, the probability of phase commutation failure is less than 70%, and in this case, the probability of phase commutation failure is low or not high.

Further, with respect to the three-phase alternating voltage and the three-phase alternating current, sampling may be performed a plurality of times in succession, and then sin-cos decomposition detection may be performed on the sampled data, thereby calculating the commutation area of the three-phase alternating voltage and the three-phase alternating current at this time, and then the commutation area may be compared with the minimum commutation area where commutation of the system succeeds to determine the probability of occurrence of commutation failure: if the commutation area of the three-phase alternating voltage (or the three-phase alternating current) is not more than 70% of the minimum commutation area of the three-phase alternating voltage (or the three-phase alternating current) of which the system commutation succeeds, the situation that the probability of the occurrence of the commutation failure is high is considered; if the commutation area of the three-phase ac voltage (or three-phase ac current) is larger than 70% of the minimum commutation area of the three-phase ac voltage (or three-phase ac current) for which the commutation of the system is successful, the probability of commutation failure is low or not high.

For the direct current voltage and the direct current, firstly carrying out harmonic decomposition, extracting harmonic features for analysis, then carrying out commutation area calculation on each subharmonic, and evaluating the probability of commutation failure at the moment according to the commutation area coefficient of each subharmonic: if the sum of the area coefficients of each subharmonic commutation is more than 10%, the commutation failure probability is high; if the sum of the area coefficients of each harmonic commutation is less than 10%, the commutation failure probability is low or not high.

The probability of phase commutation failure can also be judged by utilizing the values and the change rates of bridge arm currents detected by a current sensor CT, a voltage sensor PT and the like arranged in each bridge arm of the high-voltage direct-current transmission hybrid converter, and when the detected bridge arm currents are higher than the maximum turn-off current, the situation that the probability of phase commutation failure occurrence is high occurs. The maximum turn-off current is determined by the repeated maximum turn-off current of the turn-off pipe of the bridge arm and the buffer branch matched with the same. For example, if the turn-off transistor of the bridge arm is a crimp type IGBT (model 5SNA 3000K452300) provided by ABB corporation, and the maximum turn-off current of the turn-off transistor is 3000A, in practical application, in order to ensure a certain margin, the maximum turn-off current of the bridge arm may be designed to be less than 3000A, such as 2000A.

2) If the commutation fails, the converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-commutated bridge arm of the high-voltage direct-current transmission hybrid converter, and then the control is finished;

3) and (3) controlling the turn-off pipes of the turn-off pipe valve string of each bridge arm of the high-voltage direct-current transmission hybrid converter according to the probability of phase change failure evaluated in the step (1). If the high-voltage direct-current transmission hybrid converter is in a state with high probability of occurrence of commutation failure, a converter valve control unit of the high-voltage direct-current transmission hybrid converter sends a turn-off signal to a turn-off pipe of a turn-off pipe valve string of a phase-commutated bridge arm of the high-voltage direct-current transmission hybrid converter in advance so as to switch operation and control modes; and if the high-voltage direct-current transmission hybrid converter is in a state with low probability of phase change failure occurrence, keeping the operation mode of the high-voltage direct-current transmission hybrid converter unchanged. When the detected bridge arm current is higher than the maximum turn-off current, the converter valve stage control unit sends a turn-off signal to a turn-off pipe of the turn-off pipe valve string to turn off, so that the phase change current is forced to change the phase from the phase-changed bridge arm to the phase-change bridge arm.

It should be noted that the probability of occurrence of commutation failure is determined by parameters of a specific converter, system resistance capability, and commutation failure hazard parameters. The parameters of the converter comprise the rated operating voltage and current grade and power grade of the converter, the parameters of a filter, the parameters of a converter transformer and the like; the system resistance is determined by a system short-circuit ratio (SCR), the larger the system short-circuit ratio is, namely the stronger the system resistance is, namely the lower the commutation failure occurrence probability is; the damage of single commutation failure is not large, and when the high-voltage direct-current power transmission system is accessed to a multi-feed-in fragile power grid, the single commutation failure of a single line easily causes cascading commutation failure, so that the power grid is split, and the damage is particularly serious; the probability of causing a cascade failure is characterized by the multi-feed interaction factor (MIIF). The larger the multi-feed interaction factor is, the stronger the coupling relation among the plurality of direct current lines is, and the larger the occurrence probability of the cascading commutation failure is.

According to the control method of the high-voltage direct-current transmission hybrid converter for resisting the commutation failure, disclosed by the invention, the amplitudes and the change rates of the same quantity of the three-phase alternating-current voltage and the three-phase alternating-current on the inverting side, the direct-current and the direct-current voltage on the direct-current side, the bridge arm current and the bridge arm voltage are analyzed by configuring the current sensor CT, the voltage sensor PT and the like, and the phase commutation failure is quickly predicted, detected, identified and correspondingly controlled according to the waveform characteristics. The control strategy of the interruptible tube in the hybrid converter is adjusted to enable the interruptible tube of the phase-commutated bridge arm to be turned off when the interruptible tube is within the current turn-off capacity of the interruptible tube, so that the phase commutation current is forced to commutate from the phase-commutated bridge arm to the phase commutation bridge arm. Therefore, the frequency of occurrence of commutation failure faults is reduced, and the commutation failure resisting capacity of the hybrid converter is improved, so that the reliability of a direct-current power grid is finally further improved, the fault rate is reduced, the transmission capacity is increased, and the promotion effect on national economy is improved.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.