A method and device for handling faults on the DC side of a voltage source converter

Abstract

The present invention discloses a method for handling a fault on the DC side of a voltage source converter, comprising: configuring a DC current limiting controller for the voltage source converter to control the DC current during a line fault, and when a fault occurs in the DC side line of the voltage source converter but has not yet been detected, limiting the current flowing from the voltage source converter to the line fault point to a safe level; after the DC side line fault is detected, controlling the current flowing from the voltage source converter to the line fault point to zero to clear the fault; and during the restart recovery process, ensuring that the voltage source converter does not flow a current exceeding a safe level to the line fault point. The present invention can realize the adaptive handling of different types of DC side line faults by the voltage source converter.

Description

Technical Field

[0001] The present invention belongs to the technical field of direct current transmission, and in particular relates to a method for processing a direct current side line fault of a voltage source converter. Background Art

[0002] With the continuous development of power electronic devices and the widespread application of DC transmission technology, hybrid DC transmission systems in which at least one converter station uses thyristor converters, at least one converter station uses voltage source converters, and flexible DC transmission systems in which converter stations at each end use voltage source converters have broad application prospects. Figure 1 As shown in the figure, it is a common two-terminal bipolar flexible DC transmission system, which consists of two DC poles, positive and negative. Each DC pole is a complete DC transmission circuit including a rectifier-end converter, an inverter-end converter, a DC line and a grounding pole.

[0003] When a DC line fault occurs, whether the DC line fault can be cleared quickly plays a very important role in the stable operation of the DC transmission system. At present, the voltage source converter generally adopts a modular multilevel converter (MMC) structure. The half-bridge MMC converter based on the conventional half-bridge sub-module (HBSM) cannot block the DC side fault. In the case that the DC side is not equipped with a DC circuit breaker or a high-power diode, the flexible DC station needs to adopt a converter topology with DC side fault clearing capability, such as a full-bridge MMC converter based on a full-bridge sub-module (FBSM) or a hybrid MMC converter based on a mixture of full-bridge and half-bridge sub-modules. For converters with the ability to clear DC side faults, Li Shaohua et al. proposed in their paper “Hybrid MMC and its DC fault ride-through strategy optimization” (Proceedings of the CSEE, 2016, 36(7): 1849-1858) that after a DC side line fault occurs, the converter is controlled to output zero DC current to clear the DC side fault. This method can effectively handle metallic instantaneous ground faults that occur in the DC side line of the voltage source converter, but it cannot effectively handle high-resistance ground faults or continuous ground faults that often occur in actual projects. For high-resistance ground faults, the detection time of the DC line fault is often long due to the relatively slow change of electrical quantities. If the current flowing from the voltage source converter to the fault point continues to increase before the DC line fault is detected and causes the voltage source converter to be overcurrent locked, the fault clearing will fail. For a persistent ground fault, since the voltage source converter will try to restore the DC voltage after the deionization process is completed, if the fault has not been actually cleared, as the DC voltage rises, the voltage source converter will re-inject current into the fault point, which may cause the voltage source converter to be overcurrent locked.

[0004] For voltage source converters that are not equipped with DC circuit breakers or high-power diodes on the DC side, there is currently no proposed method that can adapt to different types of DC side line faults. Therefore, it is necessary to study a method that can enable voltage source converters to adaptively handle different types of DC side line faults. Summary of the invention

[0005] The object of the present invention is to provide a method for handling a DC side line fault of a voltage source converter in view of the deficiencies in the prior art, so as to meet the needs of handling a DC line fault of a DC transmission system containing a voltage source converter.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] On the one hand, the present invention provides a method for handling a fault on a DC side line of a voltage source converter, wherein the voltage source converter is arranged at a rectifier end or an inverter end of any DC pole of a DC power transmission system, and the rectifier end and the inverter end are connected via a DC line, and the method comprises:

[0008] According to the DC voltage control target of the DC pole, the normal value U of the DC voltage reference value of the voltage source converter is obtained. dVref-Nom ;

[0009] When no DC side line fault is detected, the DC current limit target value I of the voltage source converter is set dclim is the first current threshold -ΔI;

[0010] Based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value;

[0011] The DC current limiting control output value is compared with the normal value U of the DC voltage reference value of the voltage source converter. dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , for the control of voltage source converters;

[0012] After the DC side line fault is detected, the DC current limit target value I dclim Set to zero to control the DC current measurement value I dc to zero and remain there until the deionization time is over;

[0013] After the deionization time is over, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom The DC current limit target value I dclim Switch from zero to -ΔI;

[0014] DC voltage reference value U of the voltage source converter dVref The voltage source converter DC voltage reference value U dVref-Nom After they are equal, the DC side line fault handling process is completed.

[0015] Preferably, the DC voltage control target of the DC pole is used to obtain the normal value U of the DC voltage reference value of the voltage source converter. dVref-Nom include:

[0016] According to the DC voltage control target of the DC pole, the DC voltage reference value U of the DC pole at the end where the voltage source converter is located is obtained. dcref ;

[0017] When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter U dVref-Nom ;

[0018] When the rectifier or inverter end of the DC pole contains two or more voltage source converters running in series, the DC pole DC voltage reference value U dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer.

[0019] Preferably, when the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

[0020] Preferably, the method further comprises: in the step of setting the DC current limiting target value I dclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

[0021] Preferably, the method further comprises: converting the calculated voltage source converter DC voltage reference value U dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

[0022] Preferably, the method further comprises: when the voltage source converter is used for DC voltage control of the DC pole, the calculated DC voltage reference value U dVref The measured DC voltage value U of the voltage source converter dV The difference after subtraction is adjusted by PI to obtain the d-axis current reference value, thereby realizing the control of the DC pole DC voltage.

[0023] Preferably, when the rectifier end or the inverter end of the DC pole includes two or more voltage source converters operating in series, one of the voltage source converters is selected as the master converter, and the other converters are slave converters, and each slave converter synchronously maintains its DC voltage reference value consistent with the DC voltage reference value of the master converter.

[0024] On the other hand, the present invention provides a device for handling a fault on a DC side line of a voltage source converter, wherein the voltage source converter is arranged at a rectifier end or an inverter end of any DC pole of a DC power transmission system, and the rectifier end and the inverter end are connected via a DC line. The device comprises: a DC voltage reference normal value acquisition unit, a DC current limiting target value setting unit, a current limiting control output unit and a DC voltage reference value setting unit, wherein:

[0025] DC voltage reference normal value acquisition unit: used to obtain the normal value U of the DC voltage reference value of the voltage source converter according to the DC voltage control target of the DC pole dVref-Nom ;

[0026] DC current limit target value setting unit: used to set the DC current limit target value I of the voltage source converter when no DC side line fault is detected dclim is the first current threshold -ΔI; after the DC side line fault is detected, the DC current limiting target value I dclim Set to zero to control the DC current measurement value I dc to zero and maintain until the deionization time ends; after the deionization time ends, the DC current limit target value I dclim Switch from zero to -ΔI;

[0027] Current limiting control output unit: used to control the current based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value;

[0028] A DC voltage reference value setting unit is used to set the DC current limiting control output value and the normal value U of the DC voltage reference value of the voltage source converter when no DC side line fault is detected or the DC side line fault is detected but the de-ionization time has not ended. dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , used for the control of the voltage source converter; after the deionization time is over, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom Climb until the DC voltage reference value U dVref The voltage source converter DC voltage reference value U dVref-Nom equal.

[0029] Preferably, the DC voltage reference normal value acquisition unit includes:

[0030] According to the DC voltage control target of the DC pole, the DC voltage reference value U of the DC pole at the end where the voltage source converter is located is obtained. dcref ;

[0031] When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter U dVref-Nom ;

[0032] When the rectifier or inverter end of the DC pole contains two or more voltage source converters running in series, the DC pole DC voltage reference value U dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer.

[0033] Preferably, when the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

[0034] Preferably, the device further comprises: a limiting unit for setting the DC current limiting target value Idclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

[0035] Preferably, the device further comprises: a bridge arm reference voltage calculation unit, which calculates the voltage source converter DC voltage reference value U dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

[0036] The beneficial effects of the present invention are:

[0037] The present invention provides a method for handling a DC side line fault of a voltage source converter, wherein a DC current limiting controller is configured for the voltage source converter to control the DC current during a line fault, and when a fault occurs in the DC side line of the voltage source converter but has not yet been detected, the current flowing from the voltage source converter to the line fault point is limited to a safe level; after the DC side line fault is detected, the current flowing from the voltage source converter to the line fault point is controlled to zero to clear the fault; during the restart recovery process, it is ensured that the voltage source converter does not flow a current exceeding a safe level to the line fault point. This method can realize the adaptive handling of different types of DC side line faults by the voltage source converter, and meet the handling needs of DC line faults of a DC transmission system containing a voltage source converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the main circuit of the two-terminal bipolar flexible direct current transmission system provided by an embodiment of the present invention;

[0039] Figure 2 is a schematic diagram of a voltage source converter topology provided by an embodiment of the present invention;

[0040] Figure 3 It is the equivalent circuit diagram of the DC side of the inverter voltage source converter in the present invention;

[0041] Figure 4 It is an equivalent circuit diagram after a fault occurs in the DC side line of the inverter-end voltage source converter in the present invention;

[0042] Figure 5 It is a flow chart of a method for handling a DC side line fault of a voltage source converter provided by an embodiment of the present invention;

[0043] Figure 6 It is a schematic diagram of the topology of two or more voltage source converters operating in series in the present invention;

[0044] Figure 7 It is a structural diagram of a voltage source converter controller equipped with a DC current limiting controller provided by the present invention;

[0045] Figure 8 The invention provides a device for processing faults of a DC side line of a voltage source converter. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0047] The present invention provides a method and device for processing a DC side line fault of a voltage source converter. The voltage source converter is arranged at the rectifier end or the inverter end of any DC pole of a DC power transmission system. The rectifier end and the inverter end are connected through a DC line. The method and device are used to realize adaptive processing of different types of DC side line faults by the voltage source converter, thereby meeting the processing needs of DC line faults of a DC power transmission system containing a voltage source converter.

[0048] Figure 1 The main circuit diagram of the two-terminal bipolar flexible direct current transmission system provided by the embodiment of the present invention is composed of two positive and negative DC poles, each of which is a complete DC transmission circuit including a rectifier-end converter, an inverter-end converter, a DC line, and a grounding electrode. The rectifier-end converter and the inverter-end converter of this embodiment are both voltage source converters. Figure 2 It is a schematic diagram of the voltage source converter topology provided by an embodiment of the present invention.

[0049] The voltage source converter adopts a modular multi-level structure and includes the following two types or one type of sub-modules:

[0050] The first type of submodule is a submodule that can output positive, negative, and zero levels in a non-latched state, such as a full-bridge submodule (FBSM).

[0051] The second type of sub-module is a sub-module that can only output positive and zero levels in a non-locked state, such as a half-bridge sub-module (HBSM), a quasi-full-bridge sub-module (SFBSM), and the like.

[0052] The topological diagram of the voltage source converter is as follows: Figure 2 As shown, U ap , U bp , U cp are the upper arm voltages of the three phases A, B, and C of the voltage source converter, U an , U bn , U cn They are the lower bridge arm voltages of phases A, B, and C respectively; L0 is the inductance of the bridge arm reactor.

[0053] The bridge arm submodule configuration methods of the voltage source converter include the following two methods:

[0054] Method 1: The upper and lower bridge arms of each phase are composed of cascaded first-type submodules;

[0055] In the second mode, the upper and lower bridge arms of each phase are hybrid bridge arms composed of two types of sub-modules, namely, the first type of sub-module and the second type of sub-module, which are cascaded, and the number of the two types of sub-modules in each bridge arm is configured in the same proportion.

[0056] For the voltage source converter, its DC side equivalent circuit can be Figure 3 Indicates that U dV represents the measured value of the DC voltage of the voltage source converter, u com represents the ideal DC voltage of the voltage source converter, L eq represents the equivalent inductance of the voltage source converter.

[0057] According to the submodule connection characteristics of the voltage source converter, it is assumed that the average capacitor voltage of the working submodule of each bridge arm is U c Same, u com It can be expressed as:

[0058]

[0059] Among them, U cN is the rated voltage of the submodule capacitor.

[0060] It can be seen that the submodule capacitor voltage U c While maintaining stability, the ideal DC voltage of the voltage source converter will be determined by the DC voltage reference value of the converter. Adjusting the DC voltage reference value of the voltage source converter can achieve control of the DC voltage output by the converter.

[0061] Taking the inverter voltage source converter as an example, the equivalent circuit after the DC side line fails is as follows: Figure 4 As shown, according to Kirchhoff's voltage law, the voltage between the inverter station and the DC line fault point satisfies the following expression:

[0062]

[0063] Among them, U f is the DC voltage at the fault point, R line , L line are the equivalent resistance and inductance of the DC line from the inverter to the fault point, L d is the inductance of the inverter-end smoothing reactor.

[0064] It can be seen from formula (2) that when a DC line fault occurs and causes U f Lower than u com After that, the inverter DC current I dc The reverse current will flow into the fault point. Due to the effect of inductive components such as DC line, smoothing reactor and bridge arm reactor, the inverter end Idc It will first drop to 0 from the initial value before the fault, and then increase in the reverse direction from 0. If the DC current continues to increase in the reverse direction to the converter overcurrent level, the converter will be locked.

[0065] When a DC line fault occurs but has not yet been detected, if the voltage source converter actively adjusts u c om, outputting a DC voltage that matches the fault point will enable the current provided by the voltage source converter to the fault point to be maintained at a safe level, ensuring that the voltage source converter does not experience overcurrent lockout.

[0066] Based on the above analysis, the embodiment of the present invention proposes a method for handling a DC side line fault of a voltage source converter, such as Figure 5 As shown, the following steps are included:

[0067] S100: Obtaining a normal value U of a DC voltage reference value of a voltage source converter according to a DC voltage control target of a DC pole dVref-Nom .

[0068] In some embodiments, when the rectifier end or the inverter end of the DC pole is a single operating voltage source converter, the specific method includes:

[0069] S111: Obtaining a DC pole DC voltage reference value U of the DC pole at the end where the voltage source converter is located according to the DC pole DC voltage control target dcref ;

[0070] S112: When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter U dVref-Nom .

[0071] In some embodiments, when using Figure 6 In the topology shown, when the rectifier or inverter end of the DC pole includes two or more voltage source converters operating in series, the specific methods include:

[0072] S121: Obtaining a DC pole DC voltage reference value U of the DC pole at the end where the voltage source converter is located according to the DC pole DC voltage control target dcref ;

[0073] S122: Set the DC voltage reference value U dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer.

[0074] S200: When no DC side line fault is detected, setting the DC current limit target value I of the voltage source converterdclim is the first current threshold -ΔI.

[0075] In some embodiments, when the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

[0076] S300: Based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value.

[0077] S400: comparing the DC current limiting control output value with the normal value U of the DC voltage reference value of the voltage source converter dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , used for the control of voltage source converters.

[0078] S500: After the DC side line fault is detected, the DC current limiting target value I dclim Set to zero to control the DC current measurement value I dc to zero and remain there until the deionization time is over.

[0079] S600: After the deionization time ends, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom The DC current limit target value I dclim Switch from zero to -ΔI.

[0080] S700: DC voltage reference value U of the voltage source converter dVref The voltage source converter DC voltage reference value U dVref-Nom After they are equal, the DC side line fault handling process is completed.

[0081] When the voltage source converter is used for DC voltage control of the DC pole, the DC voltage reference value U of the voltage source converter generated by the calculation is dVref The measured DC voltage value U of the voltage source converter dVThe difference after subtraction is adjusted by PI to obtain the d-axis current reference value, thereby realizing the control of the DC pole DC voltage.

[0082] In some embodiments, the method for handling a DC side line fault of a voltage source converter further includes, based on the above, step S600 in which the DC current limiting target value I dclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

[0083] In some embodiments, the voltage source converter DC side line fault processing method further includes: converting the calculated voltage source converter DC voltage reference value U dVref of The bridge arm voltage DC bias of the voltage source converter is used to calculate the bridge arm reference voltage. The calculation formula of the bridge arm reference voltage is:

[0084]

[0085] Where: u pj is the upper bridge arm reference voltage of phase j, u nj is the lower bridge arm reference voltage of phase j, u jo-ref is the j-phase AC reference voltage.

[0086] In some embodiments, when the rectifier end or the inverter end of the DC pole includes two or more voltage source converters operating in series, one of the voltage source converters is selected as the master converter, and the other converters are slave converters, and each slave converter synchronously maintains its DC voltage reference value consistent with the DC voltage reference value of the master converter.

[0087] Figure 7 The structure diagram of the voltage source converter controller provided by the present invention is shown as follows. Based on the current inner loop controller, the DC voltage outer loop controller and the active power outer loop controller, a DC current limiting controller is configured for the voltage source converter and a DC current limiting target value I is set. dclim The controller takes limiting the DC current to -ΔI as the control target. When the DC current is higher than -ΔI, the controller is in a positive saturation state and does not actually take effect. When the DC current drops below -ΔI, the controller will automatically take effect and adjust the DC voltage reference value so that the DC current flowing to the fault point is clamped at the level of -ΔI, thereby ensuring that the voltage source converter does not overcurrent before the fault is detected. ΔI takes a value within the corresponding range according to whether the voltage source converter operates at the inverter end or the rectifier end. When the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I. dcN ≤ΔI≤1.0I dcNWhen the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax .

[0088] When a DC line fault is detected, in order to clear the DC line fault current, it is necessary to block the voltage source converter from injecting current into the DC line fault point. To this end, the DC current limit target value I dclim Switch from -ΔI to zero, control the DC current measurement value I dc to zero and remain there until the deionization time is over.

[0089] After the deionization time is over, the voltage source converter will restore the DC voltage and set the DC voltage reference value U dVref From the current value to the normal value U of the DC voltage reference value according to the set slope dVref-Nom To avoid overcurrent during the restart recovery phase under a continuous ground fault, the DC current limiting controller can be kept enabled during the restart boost phase and the DC current limiting target value I dclim The DC current limiting controller output is used as the upper limit of the DC voltage reference value. Once the DC current reversely increases to below -ΔI during the restart boost phase, the controller will automatically limit the rise of the DC voltage reference value and clamp the DC current flowing to the fault point at the level of -ΔI. After the DC line fault is detected again, the next fault clearing is started. The DC current limiting controller is set at the DC voltage reference value U dVref Climb to the normal value U of the DC voltage reference value of the voltage source converter dVref-Nom After they are equal, exit and the DC side line fault handling process ends.

[0090] The calculated voltage source converter DC voltage reference value U dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

[0091] When the voltage source converter is used for DC voltage control of the DC pole, the DC voltage reference value U of the voltage source converter generated by the calculation is dVref The measured DC voltage value U of the voltage source converter dV After the phase subtraction, the DC voltage outer loop controller of the input voltage source converter performs closed loop control to realize the control of the DC voltage of the DC pole. When the voltage source converter is used for active power control, the active power outer loop controller is used to control the active output of the voltage source converter.

[0092] like Figure 8As shown, an embodiment of the present invention provides a device for handling a DC side line fault of a voltage source converter, comprising: a DC voltage reference normal value acquisition unit, a DC current limiting target value setting unit, a current limiting control output unit and a DC voltage reference value setting unit, wherein:

[0093] DC voltage reference normal value acquisition unit: used to obtain the normal value U of the DC voltage reference value of the voltage source converter according to the DC voltage control target of the DC pole dVref-Nom .

[0094] DC current limit target value setting unit: used to set the DC current limit target value I of the voltage source converter when no DC side line fault is detected dclim is the first current threshold -ΔI; after the DC side line fault is detected, the DC current limiting target value I dclim Set to zero to control the DC current measurement value I dc to zero and maintain until the deionization time ends; after the deionization time ends, the DC current limit target value I dclim Switch from zero to -ΔI.

[0095] Current limiting control output unit: used to control the current based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value.

[0096] A DC voltage reference value setting unit is used to set the DC current limiting control output value and the normal value U of the DC voltage reference value of the voltage source converter when no DC side line fault is detected or the DC side line fault is detected but the de-ionization time has not ended. dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , used for the control of the voltage source converter; after the deionization time is over, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom Climb until the DC voltage reference value U dVref The voltage source converter DC voltage reference value U dVref-Nom equal.

[0097] In some embodiments, the DC voltage reference normal value acquisition unit comprises: acquiring a DC voltage reference value U of the DC pole at the end where the voltage source converter is located according to the DC voltage control target of the DC pole. dcref ; When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter UdVref-Nom ;

[0098] In some embodiments, when the rectifier end or the inverter end of the DC pole includes two or more voltage source converters operating in series, the DC voltage reference normal value acquisition unit includes: acquiring the DC voltage reference value U of the DC pole at the end where the voltage source converter is located according to the DC voltage control target of the DC pole. dcref ; Set the DC voltage reference value U at the DC pole of the voltage source converter dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer.

[0099] In some embodiments, when the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

[0100] In some embodiments, the device further comprises: a limiting unit, configured to limit the DC current to a target value I dclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

[0101] In some embodiments, the device further comprises: a bridge arm reference voltage calculation unit, which calculates the voltage source converter DC voltage reference value U dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

[0102] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for handling a fault on a DC side line of a voltage source converter, wherein the voltage source converter is arranged at a rectifier end or an inverter end of any DC pole of a DC power transmission system, and the rectifier end and the inverter end are connected via a DC line, characterized in that: The method comprises: According to the DC voltage control target of the DC pole, the normal value U of the DC voltage reference value of the voltage source converter is obtained. dVref-Nom Specifically including: obtaining the DC voltage reference value U of the DC pole at the end of the voltage source converter according to the DC voltage control target of the DC pole dcref ; When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter U dVref-Nom When the rectifier or inverter end of the DC pole contains two or more voltage source converters running in series, the DC pole DC voltage reference value U dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer; When no DC side line fault is detected, the DC current limit target value I of the voltage source converter is set dclim is the first current threshold -ΔI; Based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value; The DC current limiting control output value is compared with the normal value U of the DC voltage reference value of the voltage source converter. dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , for the control of voltage source converters; After the DC side line fault is detected, the DC current limit target value I dclim Set to zero to control the DC current measurement value I dc to zero and remain there until the deionization time is over; After the deionization time is over, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom The DC current limit target value I dclim Switch from zero to -ΔI; DC voltage reference value U of the voltage source converter dVref The voltage source converter DC voltage reference value U dVref-Nom After they are equal, the DC side line fault handling process is completed.

2. A method for handling a DC side line fault of a voltage source converter according to claim 1, characterized in that: When the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

3. A method for handling a DC side line fault of a voltage source converter according to claim 1, characterized in that: The method further comprises: In the above method, the DC current limiting target value I dclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

4. A method for handling a DC side line fault of a voltage source converter according to claim 1, characterized in that: The method further comprises: The calculated voltage source converter DC voltage reference value U dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

5. A method for handling a DC side line fault of a voltage source converter according to claim 1, characterized in that: The method further comprises: When the voltage source converter is used for DC voltage control of the DC pole, the DC voltage reference value U of the voltage source converter generated by the calculation is dVref The measured DC voltage value U of the voltage source converter dV The difference after subtraction is adjusted by PI to obtain the d-axis current reference value, thereby realizing the control of the DC pole DC voltage.

6. A method for handling a DC side line fault of a voltage source converter according to claim 1, characterized in that: When the rectifier end or inverter end of the DC pole includes two or more voltage source converters operating in series, one of the voltage source converters is selected as the master converter, and the other converters are slave converters. Each slave converter synchronously maintains its DC voltage reference value consistent with the DC voltage reference value of the master converter.

7. A device for handling faults on the DC side of a voltage source converter, wherein the voltage source converter is arranged at the rectifier end or the inverter end of any DC pole of a DC power transmission system, and the rectifier end and the inverter end are connected via a DC line, characterized in that: The device comprises: DC voltage reference normal value acquisition unit: used to obtain the normal value U of the DC voltage reference value of the voltage source converter according to the DC voltage control target of the DC pole dVref-Nom Specifically including: obtaining the DC voltage reference value U of the DC pole at the end of the voltage source converter according to the DC voltage control target of the DC pole dcref ; When the rectifier or inverter end of the DC pole includes a voltage source converter, U dcref As the normal value of the DC voltage reference value of the voltage source converter U dVref-Nom When the rectifier or inverter end of the DC pole contains two or more voltage source converters running in series, the DC pole DC voltage reference value U dcref The normal value U of the DC voltage reference value of each operating voltage source converter is allocated according to the total number M of voltage source converters in series operation. dVref-Nom ,in M is a positive integer; DC current limit target value setting unit: used to set the DC current limit target value I of the voltage source converter when no DC side line fault is detected dclim is the first current threshold -ΔI; after the DC side line fault is detected, the DC current limiting target value I dclim Set to zero to control the DC current measurement value I dc to zero and maintain until the deionization time ends; after the deionization time ends, the DC current limit target value I dclim Switch from zero to -ΔI; Current limiting control output unit: used to control the current based on the DC current measurement value I dc The DC current limit target value I dclim The difference after subtraction is subjected to PI control to obtain the DC current limiting control output value; A DC voltage reference value setting unit is used to set the DC current limiting control output value and the normal value U of the DC voltage reference value of the voltage source converter when no DC side line fault is detected or the DC side line fault is detected but the de-ionization time has not ended. dVref-Nom The smaller of the two is used as the DC voltage reference value U of the voltage source converter dVref , used for the control of the voltage source converter; after the deionization time is over, the DC voltage reference value U dVref The current value is set to the normal value U of the DC voltage reference value of the voltage source converter according to the set slope. dVref-Nom Climb until the DC voltage reference value U dVref The voltage source converter DC voltage reference value U dVref-Nom equal.

8. A voltage source converter DC side line fault processing device according to claim 7, characterized in that: When the voltage source converter operates at the inverter end, the value range of ΔI is 0.1I dcN ≤ΔI≤1.0I dcN When the voltage source converter operates at the rectifier end, the value range of ΔI is (I dcref +0.1I dcN )≤ΔI≤I dcmax ; Among them: I dcN is the DC current rating, I dcref is the DC current reference value of the DC pole, I dcmax It is the upper limit of continuous operation of DC current.

9. A voltage source converter DC side line fault processing device according to claim 7, characterized in that: The device also includes: The limiting unit is used to set the DC current limiting target value I dclim When switching from zero to -ΔI, the DC current limiting control output value is used as the DC voltage reference value U of the voltage source converter. dVref upper limit.

10. A voltage source converter DC side line fault processing device according to claim 7, characterized in that: The device also includes: The bridge arm reference voltage calculation unit calculates the DC voltage reference value U of the voltage source converter generated by the calculation dVref of The bridge arm reference voltage is calculated as the bridge arm voltage DC bias of the voltage source converter.

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