WO2024027088A1 - 考虑换相裕度的多馈入系统换相失败预测协调控制方法 - Google Patents

考虑换相裕度的多馈入系统换相失败预测协调控制方法 Download PDF

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WO2024027088A1
WO2024027088A1 PCT/CN2022/142192 CN2022142192W WO2024027088A1 WO 2024027088 A1 WO2024027088 A1 WO 2024027088A1 CN 2022142192 W CN2022142192 W CN 2022142192W WO 2024027088 A1 WO2024027088 A1 WO 2024027088A1
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phase
commutation
voltage
commutation failure
zero sequence
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PCT/CN2022/142192
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French (fr)
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汤奕
戴剑丰
顾锐
钱俊良
周吉
郝珊珊
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东南大学溧阳研究院
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • the present invention relates to power system safety and stability analysis and control, in particular to a multi-feed system commutation failure prediction coordinated control method considering commutation margin.
  • High-voltage DC transmission based on the grid-commutated converter type has the advantages of large capacity and long-distance transmission and has been widely used in our country.
  • my country's East China Power Grid and China Southern Power Grid have connected multiple UHV DC lines, forming a typical multi-feed DC transmission system.
  • multi-feed DC systems the interactions between AC and DC systems are complex.
  • the sequential commutation failures of multiple DC circuits induced by a DC fault are more serious than the single commutation failure and continuous commutation failure of a single DC circuit.
  • the commutation failure of a single DC circuit causes a decrease in transmission power, and the successive commutation failures between multiple DC circuits will cause power shortages in multiple DC landing areas, thus seriously threatening the safe and stable operation of the load center power grid. Therefore, in view of the typical scenarios of successive commutation failures in multi-feed DC systems, the dominant factors of successive commutation failures in different scenarios can be analyzed, so that accurate assessment of multi-phase successive commutation failures can be achieved, and the control strategies of each DC system can be further optimized to suppress successive commutations. phase failure, thereby ensuring the safe and stable operation of the receiving end power grid and the good development of the national economy.
  • the present invention proposes a commutation failure prediction and coordinated control method for multi-fed DC systems that considers commutation margin, ensuring that the risk of commutation failure is higher and the DC consequent commutation is suppressed.
  • the invention can effectively suppress the failure of commutation in a multi-feed DC system.
  • the multi-feed system commutation failure prediction coordinated control method considering commutation margin of the present invention includes the following steps:
  • Step (1) Perform asymmetric fault detection and symmetric fault detection on the inverter side, and implement commutation failure prediction control CFPREV start output based on the detected voltage amplitude;
  • Step (2) Detect the arc extinction angle value of each DC system, perform normalization processing, and divide the minimum arc extinction angle by the maximum arc extinction angle to obtain the conversion coefficient;
  • Step (3) Select the DC system with the largest current extinction angle value for coordinated control, and multiply the output proportional coefficient of the DC system by the conversion coefficient to achieve the coordinated output of the commutation failure prediction control CFPREV.
  • step (1) the asymmetric fault detection includes the following steps:
  • Equation (1) the three-phase voltage is represented by positive sequence, negative sequence and zero sequence voltage, and its mathematical expression is as shown in Equation (1):
  • u a (t), u b (t), u c (t) respectively represent the three-phase voltage of abc, U, ⁇ , are the voltage peak value, angular frequency and initial phase angle respectively; the subscripts 1, 2 and 0 represent positive sequence, negative sequence and zero sequence respectively;
  • equation (3) the mathematical expression of zero sequence voltage u 0 at any time is as shown in equation (3);
  • the zero sequence voltage u 0 after the fault will be compared with the asymmetric fault module startup value DIFF_LEVEL after taking the absolute value; when the zero sequence voltage u 0 is greater than the asymmetric fault module startup value DIFF_LEVEL
  • the commutation failure prediction control CFPREV is multiplied by the output proportional coefficient CFPREVk according to the zero sequence voltage u 0 , the trigger angle is output.
  • step (1) the symmetrical fault detection includes the following steps:
  • the ⁇ component detection method detects various types of faults; after the commutation bus voltage is transformed by Clark transformation, the assignment of the rotation vector u ⁇ is calculated.
  • the specific calculation formulas are as shown in Equations (4) and (5):
  • the ⁇ component u ⁇ is actually the expression of the difference between the phase voltages of each phase; the phase voltages subtract and the zero sequence components cancel; no matter what kind of fault occurs, the ⁇ component u ⁇ is only represented by the AC voltage
  • the positive sequence component and negative sequence component are calculated, excluding the zero sequence component; the ⁇ component u ⁇ must cooperate with the zero sequence component fault detection algorithm to cover various types of grounded and ungrounded faults;
  • step (2) the calculation method of the conversion coefficient is as follows:
  • the arc extinction angle ⁇ i of each DC system is detected and normalized based on the steady-state data.
  • the arc extinction angle of each DC system after the unitary processing is ⁇ ipu :
  • the method of the present invention detects asymmetry and symmetry faults on the inverter side based on commutation failure prediction control, and outputs a certain trigger angle according to the detected voltage value.
  • the arc extinction angle of each DC circuit is detected in real time and normalized.
  • the smallest arc extinction angle in each DC circuit is divided by the maximum arc extinction angle to obtain the conversion coefficient.
  • the DC system with the largest arc extinction angle index is selected for coordinated control.
  • Figure 1 is the pole control logic diagram of the inverter side of the DC system
  • Figure 2 is a workflow diagram of the coordinated control method for commutation failure prediction in a multi-feed system
  • Figure 3 shows the arc extinction angle curve of each DC system under predictive control without commutation failure
  • Figure 4 shows the extinction angle curve of each DC system with commutation failure predictive control but no coordinated control
  • Figure 5 shows the arc extinction angle curve of each DC system under the coordinated control of commutation failure prediction
  • Figure 6 shows the conversion coefficient curve of each DC system under commutation failure prediction coordinated control.
  • the transient response after a fault of the inverter side AC system is mainly related to pole control.
  • the current pole control logic of the inverter side of the DC system is shown in Figure 1.
  • the fixed arc extinction angle control and the commutation failure prediction control cooperate with each other to output the trigger angle in advance to increase the commutation margin.
  • Fixed arc extinction angle control ensures that the system arc extinction angle is within a safe margin by detecting the arc extinction angle of the DC system in real time.
  • the commutation failure prediction control detects the commutation bus voltage on the inverter side in real time to determine the fault, and outputs a certain advance trigger angle based on the severity of the fault.
  • a, b, c respectively represent phase a, phase b and phase c of the power grid; U a , U b and U c represent the measured AC voltage on the converter and inverter side; DIFF_LEVEL and ABZ_LEVEL represent single-phase and three-phase fault detection respectively. Threshold, the lower the start threshold, the more frequent the commutation failure prediction control starts; commutation failure prediction control CFPREVk represents the commutation failure prediction control output gain coefficient, the higher the value, the greater the output early triggering angle; AMIN represents the output Advance trigger angle.
  • ⁇ 1pu represents the arc extinction angle of each DC system detected in real time
  • ⁇ ipu represents the arc extinction angle of each DC system under steady state.
  • the commutation failure prediction and coordinated control method of multi-feedback systems considering commutation margin includes the following steps: Step (1) Perform asymmetric fault detection and symmetric fault detection on the inverter side, and detect the voltage amplitude according to the detected voltage amplitude. Realize commutation failure prediction control CFPREV start output;
  • step (1) the asymmetric fault detection includes the following steps:
  • Equation (1) the three-phase voltage is represented by positive sequence, negative sequence and zero sequence voltage, and its mathematical expression is as shown in Equation (1):
  • u a (t), u b (t), u c (t) respectively represent the three-phase voltage of abc, U, ⁇ , are the voltage peak value, angular frequency and initial phase angle respectively; the subscripts 1, 2 and 0 represent positive sequence, negative sequence and zero sequence respectively;
  • equation (3) the mathematical expression of zero sequence voltage u 0 at any time is as shown in equation (3);
  • the zero sequence voltage u 0 after the fault will be compared with the asymmetric fault module startup value DIFF_LEVEL after taking the absolute value; when the zero sequence voltage u 0 is greater than the asymmetric fault module startup value DIFF_LEVEL
  • the commutation failure prediction control CFPREV is multiplied by the output proportional coefficient CFPREVk according to the zero sequence voltage u 0 , the trigger angle is output.
  • step (1) the symmetrical fault detection includes the following steps:
  • the ⁇ component detection method detects various types of faults; after the commutation bus voltage is transformed by Clark transformation, the assignment of the rotation vector u ⁇ is calculated.
  • the specific calculation formulas are as shown in Equations (4) and (5):
  • the ⁇ component u ⁇ is actually the expression of the difference between the phase voltages of each phase; the phase voltages subtract and the zero sequence components cancel; no matter what kind of fault occurs, the ⁇ component u ⁇ is only represented by the AC voltage
  • the positive sequence component and negative sequence component are calculated, excluding the zero sequence component; the ⁇ component u ⁇ must cooperate with the zero sequence component fault detection algorithm to cover various types of grounded and ungrounded faults;
  • Step (2) Detect the arc extinction angle value of each DC system, perform normalization processing, and divide the minimum arc extinction angle by the maximum arc extinction angle to obtain the conversion coefficient; the calculation method of the conversion coefficient is as follows:
  • the arc extinction angle ⁇ i of each DC system is detected and normalized based on the steady-state data.
  • the arc extinction angle of each DC system after the unitary processing is ⁇ ipu :
  • the extinction angle curves of the two-circuit DC systems under the two methods of not using commutation failure prediction control CFPREV and using commutation failure prediction control CFPREV but without coordinated control are shown in Figure 3 and Figure 4 respectively.
  • Figure 3 shows the extinction angle curve of each DC system under predictive control without commutation failure. It can be seen from Figure 3 that due to a ground fault on the inverter side of DC system 2, the first commutation failure occurred in DC system 2 at 1.008s.
  • DC system 2 Due to the coupling relationship between multi-fed DC systems, DC system 2 will absorb a large amount of reactive power after commutation failure, which will cause voltage stability problems on the inverter side of DC system 1, and then cause two consecutive commutation failures in DC system 1. .
  • Figure 4 shows the arc extinction angle curve of each DC system with commutation failure prediction control but without coordinated control. It can be seen from Figure 4 that after commutation failure prediction control CFPREV control is adopted, due to the commutation failure prediction control CFPREV of the two circuits acting separately The output trigger angle increases the commutation margin of the respective DC systems. Although the commutation failures of DC system 1 and DC system 2 are not suppressed, there is a certain delay due to the commutation failure prediction control CFPREV. The failure of commutation failure prediction control CFPREV control to effectively suppress successive commutation failures is mainly due to the fact that each controller acts independently without considering the impact on the rest of the DC system. Therefore, coordinated control of the controllers is required.
  • the arc extinction angle of each DC system after adopting commutation failure prediction coordinated control is shown in Figure 5. It can be seen that after adopting coordinated control, the successive commutation failures of DC system 1 have been effectively suppressed. At the same time, due to the stable recovery of DC system 1, stable reactive power support is provided for DC system 2, thereby effectively avoiding subsequent commutation failure of DC system 2.
  • the effective suppression of successive commutation failures of DC system 1 mainly comes from the coordinated control of DC systems 1 and 2 based directly on the extinction angle indicator.
  • the conversion coefficient curve of each DC system under the commutation failure prediction coordinated control is shown in Figure 6.

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Abstract

本发明公开了考虑换相裕度的多馈入系统换相失败预测协调控制方法，包括如下步骤：步骤(1)对逆变侧进行不对称故障检测和对称故障检测，并根据检测电压幅值实现换相失败预测控制CFPREV启动输出；步骤(2)检测各回直流系统的熄弧角数值，并进行标幺化处理，并将最小的熄弧角除以最大的熄弧角得到折算系数；步骤(3)选取当前熄弧角数值最大的直流系统进行协调控制，将直流系统的输出比例系数乘以所述折算系数，从而实现换相失败预测控制CFPREV的协调输出，本发明保证了换相失败风险较高回直流的抑制相继换相失败的效果，能够有效的抑制多馈入直流系统相继换相失败。

Description

考虑换相裕度的多馈入系统换相失败预测协调控制方法 技术领域
本发明涉及电力系统安全稳定分析与控制，特别是考虑换相裕度的多馈入系统换相失败预测协调控制方法。
背景技术
基于电网换相换流器型的高压直流输电引起大容量、传输远距离传输的优势在我国得到广泛应用。目前，我国华东电网，南方电网已接入多回特高压直流线路，形成了典型的多馈入直流输电系统。对于多馈入直流系统，各回交直流系统相互作用错综复杂，一回直流故障诱发的多回直流相继换相失败相较单回直流的单次换相失败和连续换相失败更为严重。单回直流的换相失败引发传输功率下降，而多回直流间的相继换相失败会造成多个直流的落点区域的功率缺额，从而严重威胁了负荷中心电网的安全稳定运行。因此针对多馈入直流系统相继换相失败的典型场景，分析不同场景下相继换相失败的主导因素，从而可以实现多相继换相失败的准确评估，进一步优化各回直流系统控制策略以抑制相继换相失败，从而确保受端电网安全稳定运行及国民经济良好的发展。
在相继换相失败应对策略方面，虽然针对多馈入直流系统协调控制策略研究较多，但大多集中在多馈入直流系统相关参数的优化规划研究。其中优化规划策略下恢复优先级指标有效性难以验证，一部分优化算法也较为复杂。同时目前的研究往往都是基于特定的场景，缺乏与其他应对方法的比较，从而控制效果的适应性无法验证。而基于实际控制保护装置的协调控制策略研究较为缺乏，有必要对多馈入直流系统的协调进一步研究以弥补优化规划方法的不足。
发明内容
本发明针对多馈入直流系统相继换相失败的问题，提出了考虑换相裕度的多馈入系统换相失败预测协调控制方法，保证了换相失败风险较高回直流的抑制相继换相失败的效果，本发明能够有效的抑制多馈入直流系统相继换相失败。
本发明所采用的技术方案如下：
本发明的考虑换相裕度的多馈入系统换相失败预测协调控制方法，包括如下步骤：
步骤(1)对逆变侧进行不对称故障检测和对称故障检测，并根据检测电压幅值实现换相失败预测控制CFPREV启动输出；
步骤(2)检测各回直流系统的熄弧角数值，并进行标幺化处理，并将最小的熄弧角除以最 大的熄弧角得到折算系数；
步骤(3)选取当前熄弧角数值最大的直流系统进行协调控制，将直流系统的输出比例系数乘以所述折算系数，从而实现换相失败预测控制CFPREV的协调输出。
步骤(1)中，所述不对称故障检测包括以下步骤：
无论系统是否故障，三相电压均用正序、负序和零序电压表示，其数学表达式如式(1)所示：
Figure PCTCN2022142192-appb-000001
式中：u a(t)、u b(t)、u c(t)分别表示abc三相电压，U、ω、
Figure PCTCN2022142192-appb-000002
分别为电压峰值、角频率和初相角；下标1、2和0分别表示正序、负序和零序；
交流系统发生单相接地短路或两相短路接地故障时，换流母线电压会出现零序分量，而发生相间短路或三相短路故障时没有零序分量，故零序分量故障检测算法适用于单相接地短路或两相短路接地故障，其计算公式如式(2)所示：
u 0(t)＝u a(t)+u b(t)+u c(t)(2)
将式(1)带入式(2)，则零序电压u 0在任意时刻的数学表达式如式(3)所示；
Figure PCTCN2022142192-appb-000003
稳态时候u 0(t)为0，故障后零序电压u 0将在取绝对值后，与不对称故障模块启动值DIFF_LEVEL进行比较；当零序电压u 0大于不对称故障模块启动值DIFF_LEVEL时，换相失败预测控制CFPREV根据零序电压u 0大小乘以输出比例系数CFPREVk后输出触发角度。
步骤(1)中，所述对称故障检测包括以下步骤：
αβ分量检测法检测各种类型的故障；换流母线电压经克拉克变换Clark变换后，计算旋转矢量的赋值u αβ，具体计算公式如式(4)和式(5)所示：
Figure PCTCN2022142192-appb-000004
Figure PCTCN2022142192-appb-000005
将式(4)代入式(5)，整理得：
Figure PCTCN2022142192-appb-000006
由式(6)可知，αβ分量u αβ实际上是各相相电压之差的表达式；相电压相减，零序分量相消；无论发生何种故障，αβ分量u αβ仅由交流电压的正序分量和负序分量计算而得，不含零序分量；αβ分量u αβ必须与零序分量故障检测算法相互配合，才能覆盖接地与不接地的各类型故障；
用电压αβ分量u αβ减去1，然后将得到的差值和对称故障模块启动值ABZ_LEVEL进行比较；当差值大于对称故障模块启动值ABZ_LEVEL时，换相失败预测控制CFPREV根据差值乘以输出比例系数CFPREVk后输出触发角度。
步骤(2)中，所述折算系数的计算方法如下：
检测各回直流系统的熄弧角γ i，并基于稳态数据进行标幺化处理，标幺化处理后的各回直流系统熄弧角为γ ipu：
γ ipu＝γ i/15°       (7)
选取各回直流系统熄弧角最小值γ minpu和各回直流系统熄弧角最大值γ maxpu，相除得到折算系数coefficient：
coefficient＝γ minpu/γ maxpu(8)。
本发明的方法基于换相失败预测控制对逆变侧不对称、对称故障进行检测，并根据检测电压数值输出一定的触发角度。同时实时检测各回直流系统熄弧角并进行标幺化处理， 选取各回直流中最小的熄弧角与最大的熄弧角相除得到折算系数。最后选取当前熄弧角指标最大的直流系统进行协调控制，通过将该回直流系统换相失败预测控制CFPREV输出比例系数CFPREVk乘以折算系数，即可削弱该回直流对其他直流系统的影响，从而有利于回直流系统抑制相继换相失败的效果。
附图说明
图1为直流系统逆变侧极控逻辑图；
图2为多馈入系统换相失败预测协调控制方法工作流程图；
图3为无换相失败预测控制下各回直流系统熄弧角曲线；
图4为有换相失败预测控制但未协调控制下各回直流系统熄弧角曲线；
图5为换相失败预测协调控制下各回直流系统熄弧角曲线；
图6为换相失败预测协调控制下各回直流系统折算系数曲线。
具体实施方式
以下将结合具体实施例对本发明提供的技术方案进行详细说明，应理解下述具体实施方式仅用于说明本发明而不用于限制本发明的范围。
逆变侧交流系统故障后的暂态响应主要与极控制有关，目前直流系统逆变侧极控逻辑如图1所示。其中定熄弧角控制和换相失败预测控制相互配合，输出提前触发角度以增加换相裕度。定熄弧角控制通过实时检测直流系统熄弧角，确保系统熄弧角处于安全的裕度。而换相失败预测控制则对逆变侧换流母线电压的实时检测从而判定故障，并基于故障严重程度，输出一定的提前触发角度。然后通过与定熄弧角控制输出相结合，从而能够及时输出充裕的提前触发角度，抑制换相失败的发生。a、b、c分别表示电网的a相、b相和c相；U a、U b、U c表示量测得的换逆变侧交流电压；DIFF_LEVEL和ABZ_LEVEL分别表示单相、三相故障检测门槛阈值，启动门槛阈值越低则换相失败预测控制启动越频繁；换相失败预测控制CFPREVk表示换相失败预测控制输出增益系数，其数值越高，输出提前触发角度越大；AMIN表示输出的提前触发角度。γ 1pu表示实时检测的各回直流系统的熄弧角，γ ipu表示各回直流系统稳态下的熄弧角。
参见图2，考虑换相裕度的多馈入系统换相失败预测协调控制方法，包括如下步骤：步骤(1)对逆变侧进行不对称故障检测和对称故障检测，并根据检测电压幅值实现换相失败预测控制CFPREV启动输出；
步骤(1)中，所述不对称故障检测包括以下步骤：
无论系统是否故障，三相电压均用正序、负序和零序电压表示，其数学表达式如式(1)所示：
Figure PCTCN2022142192-appb-000007
式中：u a(t)、u b(t)、u c(t)分别表示abc三相电压，U、ω、
Figure PCTCN2022142192-appb-000008
分别为电压峰值、角频率和初相角；下标1、2和0分别表示正序、负序和零序；
交流系统发生单相接地短路或两相短路接地故障时，换流母线电压会出现零序分量，而发生相间短路或三相短路故障时没有零序分量，故零序分量故障检测算法适用于单相接地短路或两相短路接地故障，其计算公式如式(2)所示：
u 0(t)＝u a(t)+u b(t)+u c(t)(2)
将式(1)带入式(2)，则零序电压u 0在任意时刻的数学表达式如式(3)所示；
Figure PCTCN2022142192-appb-000009
稳态时候u 0(t)为0，故障后零序电压u 0将在取绝对值后，与不对称故障模块启动值DIFF_LEVEL进行比较；当零序电压u 0大于不对称故障模块启动值DIFF_LEVEL时，换相失败预测控制CFPREV根据零序电压u 0大小乘以输出比例系数CFPREVk后输出触发角度。
步骤(1)中，所述对称故障检测包括以下步骤：
αβ分量检测法检测各种类型的故障；换流母线电压经克拉克变换Clark变换后，计算旋转矢量的赋值u αβ，具体计算公式如式(4)和式(5)所示：
Figure PCTCN2022142192-appb-000010
Figure PCTCN2022142192-appb-000011
将式(4)代入式(5)，整理得：
Figure PCTCN2022142192-appb-000012
由式(6)可知，αβ分量u αβ实际上是各相相电压之差的表达式；相电压相减，零序分量相消；无论发生何种故障，αβ分量u αβ仅由交流电压的正序分量和负序分量计算而得，不含零序分量；αβ分量u αβ必须与零序分量故障检测算法相互配合，才能覆盖接地与不接地的各类型故障；
用电压αβ分量u αβ减去1，然后将得到的差值和对称故障模块启动值ABZ_LEVEL进行比较；当差值大于对称故障模块启动值ABZ_LEVEL时，换相失败预测控制CFPREV根据差值乘以输出比例系数CFPREVk后输出触发角度。
步骤(2)检测各回直流系统的熄弧角数值，并进行标幺化处理，并将最小的熄弧角除以最大的熄弧角得到折算系数；折算系数的计算方法如下：
检测各回直流系统的熄弧角γ i，并基于稳态数据进行标幺化处理，标幺化处理后的各回直流系统熄弧角为γ ipu：
γ ipu＝γ i/15°    (7)
选取各回直流系统熄弧角最小值γ minpu和各回直流系统熄弧角最大值γ maxpu，相除得到折算系数coefficient：
coefficient＝γ minpu/γ maxpu(8)
为验证本发明所提出的直流系统换相失败预测控制启动值自适应设置方法抑制换相失败的有效性，基于PSCAD/EMTDC中CIGRE HVDC标准测试模型搭建典型的双馈入直流系统进行了电磁暂态仿真分析。其中直流系统1的短路比为2，直流系统2的短路比为2.5。
1)未进行协调控制的换相失败预测控制抑制相换相失败效果分析
在直流系统2的逆变侧换流母线处于1.0s设置持续时间0.2s单相接地故障，地电感值L f＝0.6H。未采用换相失败预测控制CFPREV与采用换相失败预测控制CFPREV但未协调 控制两种方法下两回直流系统的熄弧角曲线分别如图3、图4所示。图3为无换相失败预测控制下各回直流系统熄弧角曲线，由图3可以看出，由于直流系统2逆变侧发生接地故障，直流系统2于1.008s发生了首次换相失败。由于多馈入直流系统间的耦合关系，直流系统2换相失败后将吸收大量无功功率，从而引发直流系统1逆变侧电压稳定问题，进而引发直流系统1发生了两次相继换相失败。
图4为有换相失败预测控制但未协调控制下各回直流系统熄弧角曲线，由图4可以看出，采用换相失败预测控制CFPREV控制后，由于两回换相失败预测控制CFPREV分别作用输出触发角度，增加了各自直流系统的换相裕度，直流系统1和直流系统2的换相失败虽然没有得到抑制，但是由于换相失败预测控制CFPREV的作用都有了一定的延迟。采用换相失败预测控制CFPREV控制未能有效抑制相继换相失败主要源于各回控制器单独作用，没有考虑对其余直流系统的影响，因此需要对控制器进行协调控制。
2)换相失败预测协调控制抑制相换相失败效果分析
采用换相失败预测协调控制后各回直流系统熄弧角如图5所示。可以看出，采用协调控制后，直流系统1的相继换相失败均得到了有效的抑制。同时由于直流系统1的稳定恢复，给直流系统2提供了稳定的无功支撑，从而有效的避免了直流系统2的后续换相失败。直流系统1的相继换相失败的有效抑制主要源于直流系统1、2直接基于熄弧角指标的协调控制。换相失败预测协调控制下各回直流系统折算系数曲线如图6所示，通过降低相对较为稳定直流系统换相失败预测控制CFPREV的输出，从而保证了换相失败风险更大回直流系统抑制相继换相失败效果。

Claims (4)

  1. 考虑换相裕度的多馈入系统换相失败预测协调控制方法，其特征在于，包括如下步骤：步骤(1)对逆变侧进行不对称故障检测和对称故障检测，并根据检测电压幅值实现换相失败预测控制CFPREV启动输出；
    步骤(2)检测各回直流系统的熄弧角数值，并进行标幺化处理，并将最小的熄弧角除以最大的熄弧角得到折算系数；
    步骤(3)选取当前熄弧角数值最大的直流系统进行协调控制，将直流系统的输出比例系数乘以所述折算系数，从而实现换相失败预测控制CFPREV的协调输出。
  2. 根据权利要求1所述的考虑换相裕度的多馈入系统换相失败预测协调控制方法，其特征在于，步骤(1)中，所述不对称故障检测包括以下步骤：
    无论系统是否故障，三相电压均用正序、负序和零序电压表示，其数学表达式如式(1)所示：
    Figure PCTCN2022142192-appb-100001
    式中：u a(t)、u b(t)、u c(t)分别表示abc三相电压，U、ω、
    Figure PCTCN2022142192-appb-100002
    分别为电压峰值、角频率和初相角；下标1、2和0分别表示正序、负序和零序；
    交流系统发生单相接地短路或两相短路接地故障时，换流母线电压会出现零序分量，而发生相间短路或三相短路故障时没有零序分量，故零序分量故障检测算法适用于单相接地短路或两相短路接地故障，其计算公式如式(2)所示：
    u 0(t)＝u a(t)+u b(t)+u c(t)  (2)
    将式(1)带入式(2)，则零序电压u 0在任意时刻的数学表达式如式(3)所示；
    Figure PCTCN2022142192-appb-100003
    稳态时候u 0(t)为0，故障后零序电压u 0将在取绝对值后，与不对称故障模块启动值DIFF_LEVEL进行比较；当零序电压u 0大于不对称故障模块启动值DIFF_LEVEL时，换相失败预测控制CFPREV根据零序电压u 0大小乘以输出比例系数CFPREVk后输出触发角度。
  3. 根据权利要求1所述的考虑换相裕度的多馈入系统换相失败预测协调控制方法，其特征在于，步骤(1)中，所述对称故障检测包括以下步骤：
    αβ分量检测法检测各种类型的故障；换流母线电压经克拉克变换Clark变换后，计算旋转矢量的赋值u αβ，具体计算公式如式(4)和式(5)所示：
    Figure PCTCN2022142192-appb-100004
    Figure PCTCN2022142192-appb-100005
    将式(4)代入式(5)，整理得：
    Figure PCTCN2022142192-appb-100006
    由式(6)可知，αβ分量u αβ实际上是各相相电压之差的表达式；相电压相减，零序分量相消；无论发生何种故障，αβ分量u αβ仅由交流电压的正序分量和负序分量计算而得，不含零序分量；αβ分量u αβ必须与零序分量故障检测算法相互配合，才能覆盖接地与不接地的各类型故障；
    用电压αβ分量u αβ减去1，然后将得到的差值和对称故障模块启动值ABZ_LEVEL进行比较；当差值大于对称故障模块启动值ABZ_LEVEL时，换相失败预测控制CFPREV根据差值乘以输出比例系数CFPREVk后输出触发角度。
  4. 根据权利要求1所述的考虑换相裕度的多馈入系统换相失败预测协调控制方法，其特征在于，步骤(2)中，所述折算系数的计算方法如下：
    检测各回直流系统的熄弧角γ i，并基于稳态数据进行标幺化处理，标幺化处理后的各回直流系统熄弧角为γ ipu：
    γ ipu＝γ i/15°  (7)
    选取各回直流系统熄弧角最小值γ min pu和各回直流系统熄弧角最大值γ max pu，相除得到折算系数coefficient：
    coefficient＝γ min pu/γ max pu  (8)。
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