CN113036737B - Flexible current limiter capable of being connected in series on direct current circuit and control method thereof - Google Patents

Flexible current limiter capable of being connected in series on direct current circuit and control method thereof Download PDF

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CN113036737B
CN113036737B CN202110317326.7A CN202110317326A CN113036737B CN 113036737 B CN113036737 B CN 113036737B CN 202110317326 A CN202110317326 A CN 202110317326A CN 113036737 B CN113036737 B CN 113036737B
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郑峰
林佳壕
张锦松
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Lanzhou Power Supply Co Of State Grid Gansu Electric Power Co
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H9/00Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
    • H02H9/02Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
    • H02H9/021Current limitation using saturable reactors
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for AC mains or AC distribution networks
    • H02J3/36Arrangements for transfer of electric power between AC networks via a high-tension DC link
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

本发明涉及一种可串联在直流线路上的柔性限流器,其特征在于,包括桥型电路、限流器和限流器压控整流模块;所述桥型电路包括第一二极管D1、第二二极管D2、第三二极管D3、第四二极管D4,限流电感L,可控直流偏置电源Ib;所述第一二极管D1阴极与可控直流偏置电源Ib负极和第二电感D2阴极分别连接;所述第一二极管D1阳极与第三二极管D3阴极连接;所述第三二极管D3阳极与限流电感L一端和第四二极管D4阳极分别连接;所述第四二极管D4阴极与第二二极管D2阳极连接;所述限流电感L与可控直流偏置电源Ib正极连接离。本发明通过抬升故障点电压,同时处理单极接地故障和极间短路故障,并且能柔性控制限流电感的电压,有效抑制故障电流。

Figure 202110317326

The invention relates to a flexible current limiter that can be connected in series on a DC line, which is characterized in that it includes a bridge circuit, a current limiter and a current limiter voltage-controlled rectifier module; the bridge circuit includes a first diode D 1. The second diode D2, the third diode D3 , the fourth diode D4, the current limiting inductor L, the controllable DC bias power supply Ib ; the cathode of the first diode D1 It is connected with the negative electrode of the controllable DC bias power supply I b and the negative electrode of the second inductor D 2 respectively; the anode of the first diode D 1 is connected with the negative electrode of the third diode D 3 ; the third diode D 3 The anode is connected to one end of the current limiting inductor L and the anode of the fourth diode D4 respectively; the cathode of the fourth diode D4 is connected to the anode of the second diode D2; the current limiting inductor L is connected to the controllable DC The positive pole of the bias power supply I b is connected away. By raising the voltage at the fault point, the invention simultaneously handles the single-pole grounding fault and the inter-pole short-circuit fault, and can flexibly control the voltage of the current-limiting inductor, thereby effectively suppressing the fault current.

Figure 202110317326

Description

一种可串联在直流线路上的柔性限流器及其控制方法A flexible current limiter that can be connected in series on a DC line and its control method

技术领域technical field

本发明涉及电力电子技术领域,具体涉及一种基于直流配网的新型柔性限流器及控制方法。The invention relates to the technical field of power electronics, in particular to a novel flexible current limiter and a control method based on a DC distribution network.

背景技术Background technique

本随着电力电子技术的发展,直流配电网的控制更加灵活,电能质量得到提升。在分布式电源(Distributed Generations, DGs)、电动汽车(Electric Vehicle, EV)等应用场景,直流配电网提高了电能输送的效率。然而,因为直流系统“低惯性,低阻抗”的特点,系统故障危害大、发展迅速、影响范围广。尤其是因电压源型换流站(Voltage SourceConverter, VSC)的大量使用,极间短路的故障电流幅值大且变化快,给系统保护带来巨大的挑战。因此,直流配电网保护已经成为近年来的研究热点。With the development of power electronic technology, the control of DC distribution network is more flexible, and the power quality is improved. In application scenarios such as Distributed Generations (DGs) and Electric Vehicles (EV), the DC distribution network improves the efficiency of power transmission. However, due to the characteristics of "low inertia and low impedance" in DC systems, system failures have great harm, rapid development and wide influence. In particular, due to the extensive use of Voltage Source Converters (VSCs), the fault current of inter-pole short-circuits has a large amplitude and changes rapidly, which brings huge challenges to system protection. Therefore, DC distribution network protection has become a research hotspot in recent years.

当直流线路出现短路故障,AC/DC换流站出口电容和交流系统均会向故障点放电。目前,对换流站的有效保护是直流系统故障保护的主要研究方向之一。但若换流站内部全控型晶体管(Insulated Gate Bipolar Transistor, IGBT)因自保护而闭锁,交流系统将直接向故障点放电,故障电流的数值将被维持在较高的水平,且因没有过零点而难以开断。混合型直流断路器(Hybrid DC Circuit Breaker, HDCCB)能够开断极间短路的故障电流。但需要兼顾断路器的故障响应时间和断路器的应用成本。传统的混合型直流断路器通过机械开关开断故障线路,但是故障发生后需要一定的时间提升断路器内部的绝缘强度,无法满足保护的速动性要求。因此,直流配电网故障限流器的研究具有重要意义。When a short-circuit fault occurs in the DC line, the outlet capacitor of the AC/DC converter station and the AC system will both discharge to the fault point. At present, the effective protection of converter stations is one of the main research directions of DC system fault protection. However, if the fully-controlled transistor (Insulated Gate Bipolar Transistor, IGBT) inside the converter station is blocked due to self-protection, the AC system will directly discharge to the fault point, and the value of the fault current will be maintained at a high level, and because there is no overcurrent Zero point and difficult to break. Hybrid DC Circuit Breaker (HDCCB) can break the fault current of short circuit between poles. However, it is necessary to take into account the fault response time of the circuit breaker and the application cost of the circuit breaker. The traditional hybrid DC circuit breaker disconnects the fault line through a mechanical switch, but it takes a certain amount of time to improve the insulation strength inside the circuit breaker after a fault occurs, which cannot meet the quick-action requirement of protection. Therefore, the research of fault current limiter in DC distribution network is of great significance.

近10年来,国内外学者就直流限流器已经进行了相关研究,可将直流限流器划分为两大类:超导限流器和固态限流器。现有文献分别介绍了电阻型、饱和铁心型、磁屏蔽性和电桥型超导限流器的技术原理。其中,超导限流器通态损耗小,结构简单,限流效果好,然而,现有的超导材料在相对理想的环境才能维持超导状态,运行成本较高,故障切除后需要配备容量较大的循环液氮冷却系统保证超导限流器恢复至动作前的状态;自旁路限流器通过负载转换开关和超快速机械开关将故障电流回路切换至限流支路上,并且考虑了实现限流器反复使用的措施;新型电容换相混合式直流限流器,通过电容充放电实现对应桥臂的导通和关断,节省了电力电子器件的投资。可以看出,固态限流器主要由电力电子器件组成,其通态损耗较高。同时,电力电子器件数量的增加,增加限流器的故障率,也提高了投资成本。In the past 10 years, domestic and foreign scholars have carried out relevant research on DC current limiters, which can be divided into two categories: superconducting current limiters and solid-state current limiters. The existing literature introduces the technical principles of resistance type, saturated core type, magnetic shielding and bridge type superconducting current limiter respectively. Among them, the superconducting current limiter has small on-state loss, simple structure, and good current limiting effect. However, the existing superconducting material can maintain the superconducting state in a relatively ideal environment, and the operating cost is high. After the fault is removed, it needs to be equipped with a capacity The large circulating liquid nitrogen cooling system ensures that the superconducting current limiter returns to the state before the action; the self-bypass current limiter switches the fault current loop to the current limiting branch through the load transfer switch and the ultra-fast mechanical switch, and considers The measures to realize the repeated use of the current limiter; the new type of capacitor commutation hybrid DC current limiter realizes the on and off of the corresponding bridge arm through the charging and discharging of the capacitor, which saves the investment of power electronic devices. It can be seen that the solid-state current limiter is mainly composed of power electronic devices, and its on-state loss is relatively high. At the same time, the increase in the number of power electronic devices increases the failure rate of the current limiter, and also increases the investment cost.

发明内容SUMMARY OF THE INVENTION

有鉴于此,本发明的目的在于提供一种适用于直流配电网的柔性限流器,通过抬升故障点电压,同时处理单极接地故障和极间短路故障,并且能柔性控制限流电感的电压,有效抑制故障电流。In view of this, the purpose of the present invention is to provide a flexible current limiter suitable for the DC distribution network, which can simultaneously handle the single-pole grounding fault and the inter-pole short-circuit fault by raising the fault point voltage, and can flexibly control the current-limiting inductance. voltage, effectively suppressing the fault current.

为实现上述目的,本发明采用如下技术方案:To achieve the above object, the present invention adopts the following technical solutions:

一种可串联在直流线路上的柔性限流器,包括桥型电路、限流器和限流器压控整流模块,限流器位于桥型电路桥臂之上,桥型电路并联同压控整流模块并联;所述桥型电路包括第一二极管D1、第二二极管D2、第三二极管D3、第四二极管D4,限流电感L,可控直流偏置电源Ib;所述第一二极管D1阴极与可控直流偏置电源Ib负极和第二电感D2阴极分别连接;所述第一二极管D1阳极与第三二极管D3阴极连接;所述第三二极管D3阳极与限流电感L一端和第四二极管D4阳极分别连接;所述第四二极管D4阴极与第二二极管D2阳极连接;所述限流电感L与可控直流偏置电源Ib正极连接。A flexible current limiter that can be connected in series on a DC line, including a bridge circuit, a current limiter and a current limiter voltage-controlled rectifier module, the current limiter is located on the bridge arm of the bridge circuit, and the bridge circuit is connected in parallel with the voltage control The rectifier modules are connected in parallel; the bridge circuit includes a first diode D 1 , a second diode D 2 , a third diode D 3 , a fourth diode D 4 , a current limiting inductor L, and a controllable DC Bias power supply Ib ; the cathode of the first diode D1 is connected to the cathode of the controllable DC bias power supply Ib and the cathode of the second inductor D2 respectively; the anode of the first diode D1 is connected to the third and second The cathode of the diode D3 is connected to the cathode; the anode of the third diode D3 is connected to one end of the current limiting inductor L and the anode of the fourth diode D4 respectively; the cathode of the fourth diode D4 is connected to the second diode The anode of the tube D2 is connected; the current limiting inductor L is connected to the anode of the controllable DC bias power supply Ib .

进一步的,所述柔性限流器引入带有受控源的闭环铁芯来消除限流电感的饱和,铁芯一次侧为限流器,二次侧为受控源。Further, a closed-loop iron core with a controlled source is introduced into the flexible current limiter to eliminate the saturation of the current-limiting inductance, and the primary side of the iron core is the current limiter, and the secondary side is the controlled source.

进一步的,正常运行时,桥型电路将限流器旁路,不影响系统的运行;Further, during normal operation, the bridge circuit bypasses the current limiter, which does not affect the operation of the system;

故障期间,通过桥型电路切换,限流器接入系统并给故障回路提供可变的钳位电压,进而控制AC/DC换流站出口电容的压降,抑制过大的故障电流。During the fault, through the bridge circuit switching, the current limiter is connected to the system and provides a variable clamping voltage to the fault circuit, thereby controlling the voltage drop of the capacitor at the outlet of the AC/DC converter station and suppressing the excessive fault current.

进一步的,所述柔性限流器通过整流器提供的线性电流,限流电感的钳位电压被控制在稳定的数值,将限流电感的电压Ul被作为柔性限流器换流站的控制目标;Further, the flexible current limiter uses the linear current provided by the rectifier, the clamping voltage of the current limiting inductor is controlled at a stable value, and the voltage U1 of the current limiting inductor is used as the control target of the flexible current limiter converter station;

双环控制的表达式如下:The expression for double loop control is as follows:

Figure 100002_DEST_PATH_IMAGE002
(1);
Figure 100002_DEST_PATH_IMAGE002
(1);

在式(1)中,K是放大增益,K vf 是反馈系数,u set i q2 为控制系统的输入量和扰动量;其中In formula (1), K is the amplification gain, K vf is the feedback coefficient, u set and i q2 are the input quantity and disturbance quantity of the control system; where

Figure 100002_DEST_PATH_IMAGE004
(2)。
Figure 100002_DEST_PATH_IMAGE004
(2).

进一步的,所述故障判断具体为:根据保护判据,如果直流侧电压满足U dc ≤0.8U dcn ,则直流系统的故障可以被定义为极间短路故障;Further, the fault judgment is specifically: according to the protection criterion, if the DC side voltage satisfies U dc ≤ 0.8 U dcn , the fault of the DC system can be defined as an inter-pole short-circuit fault;

若电压满足下式,则故障能够被定义为单极接地故障The fault can be defined as a single-pole earth fault if the voltage satisfies the following equation

Figure 100002_DEST_PATH_IMAGE006
(3);
Figure 100002_DEST_PATH_IMAGE006
(3);

在不同的故障条件下,柔性限流器控制系统的输入量被设定为不同的数值Under different fault conditions, the input of the flexible current limiter control system is set to different values

Figure 100002_DEST_PATH_IMAGE008
(4);
Figure 100002_DEST_PATH_IMAGE008
(4);

其中,Udcn是直流系统的额定电压,U + dc U - dc 分别为直流侧正负极的电压,U + dcn U - dcn 分别为正负极电压的额定值。m 1 m 2 m 3 是系统输入的控制系数且m i =0~1(i=1,2,3)。Among them, U dcn is the rated voltage of the DC system, U + dc , U - dc are the voltages of the positive and negative poles of the DC side, respectively, and U + dcn and U - dcn are the rated values of the positive and negative voltages, respectively. m 1 , m 2 and m 3 are control coefficients input by the system and m i =0∼1( i =1,2,3).

进一步的,所述故障期间,限流器针对针对不同故障位置,通过改变控制系数m i 的数值,改变限流器提供的钳位电压,进而改变了故障回路的故障电压,最终实现故障电流的柔性控制。Further, during the fault period, the current limiter changes the clamping voltage provided by the current limiter by changing the value of the control coefficient m i for different fault positions, thereby changing the fault voltage of the fault circuit, and finally realizing the reduction of the fault current. Flexible control.

本发明与现有技术相比具有以下有益效果:Compared with the prior art, the present invention has the following beneficial effects:

1、本发明提供的新型柔性限流器的控制方法分为新型柔性限流器所在的线路正常运行、检测到极间短路故障或单向接地故障、故障持续一段时间后进行限流电感消磁三种情况对新型柔性限流器实现控制,新型柔性限流器提高直流配电网在故障时的稳定性,简化传统限流器拓扑结构;1. The control method of the novel flexible current limiter provided by the present invention is divided into three parts: normal operation of the line where the novel flexible current limiter is located, detection of an inter-pole short-circuit fault or one-way ground fault, and degaussing the current-limiting inductance after the fault persists for a period of time. In this case, the new flexible current limiter can be controlled, and the new flexible current limiter can improve the stability of the DC distribution network in the event of a fault, and simplify the traditional current limiter topology structure;

2、本发明的柔性限流器能够同时用于处理单极接地故障和极间短路故障,应用范围更加广泛;2. The flexible current limiter of the present invention can be used to deal with single-pole grounding faults and inter-pole short-circuit faults at the same time, and has a wider application range;

3、本发明在有效限流的基础上,直流系统的故障电压能够被柔性限流器灵活调整。若是极间短路故障,系统的故障电流也可根据相关器件的电流耐受值进行调整,限流的可控性大大提高;3. On the basis of effective current limiting, the fault voltage of the DC system can be flexibly adjusted by the flexible current limiter. In the case of an inter-pole short-circuit fault, the fault current of the system can also be adjusted according to the current withstand value of the relevant devices, and the controllability of current limiting is greatly improved;

4、本发明因为闭环铁芯的作用,延长了限流电感的有效作用时间。保证了故障消失前故障电流限制的稳定性;4. The present invention prolongs the effective action time of the current limiting inductor due to the function of the closed-loop iron core. Ensure the stability of the fault current limit before the fault disappears;

5、限流器动作期间,限流电感从交流系统汲取的能量能够通过柔性限流器的逆变回路返回给电网,减小了能量的损耗。5. During the operation of the current limiter, the energy drawn by the current limiting inductor from the AC system can be returned to the power grid through the inverter loop of the flexible current limiter, reducing the energy loss.

附图说明Description of drawings

图1是本发明一实施例中新型柔性限流器桥型电路拓扑结构图;1 is a topology diagram of a novel flexible current limiter bridge circuit in an embodiment of the present invention;

图2是本发明一实施例中新型柔性限流器在系统中的整体框架图;2 is an overall frame diagram of a novel flexible current limiter in a system according to an embodiment of the present invention;

图3是本发明一实施例中检测到故障后限流动作的判断图;3 is a judgment diagram of a current-limiting action after a fault is detected in an embodiment of the present invention;

图4是本发明一实施例中故障持续一段时间时的限流电感消磁过程图;4 is a diagram of a degaussing process of a current-limiting inductor when a fault lasts for a period of time in an embodiment of the present invention;

图5是本发明一实施例中新型柔性限流器的动作流程;Fig. 5 is the action flow of the novel flexible current limiter in an embodiment of the present invention;

图6是本发明一实施例中新型柔性限流器在两种故障中的作用图。FIG. 6 is a diagram of the action of the novel flexible current limiter in two faults in an embodiment of the present invention.

具体实施方式Detailed ways

下面结合附图及实施例对本发明做进一步说明。The present invention will be further described below with reference to the accompanying drawings and embodiments.

请参照图1,本发明提供一种基于直流配网的新型柔性限流器,包括桥型电路、限流器和限流器压控整流模块,限流器位于桥型电路桥臂之上,桥型电路并联同压控整流模块并联;所述桥型电路包括第一二极管D1、第二二极管D2、第三二极管D3、第四二极管D4,限流电感L,可控直流偏置电源Ib;所述第一二极管D1阴极与可控直流偏置电源Ib负极和第二电感D2阴极分别连接;所述第一二极管D1阳极与第三二极管D3阴极连接;所述第三二极管D3阳极与限流电感L一端和第四二极管D4阳极分别连接;所述第四二极管D4阴极与第二二极管D2阳极连接;所述限流电感L与可控直流偏置电源Ib正极连接。Referring to FIG. 1, the present invention provides a new type of flexible current limiter based on a DC distribution network, including a bridge circuit, a current limiter and a current limiter voltage-controlled rectifier module, the current limiter is located on the bridge arm of the bridge circuit, The bridge circuit is connected in parallel with the voltage-controlled rectifier module; the bridge circuit includes a first diode D 1 , a second diode D 2 , a third diode D 3 , and a fourth diode D 4 . Current inductance L, controllable DC bias power supply Ib ; the cathode of the first diode D1 is connected to the cathode of the controllable DC bias power supply Ib and the cathode of the second inductor D2 respectively; the first diode The anode of D1 is connected to the cathode of the third diode D3 ; the anode of the third diode D3 is connected to one end of the current limiting inductor L and the anode of the fourth diode D4 respectively; the fourth diode D 4. The cathode is connected to the anode of the second diode D2; the current-limiting inductor L is connected to the anode of the controllable DC bias power supply Ib .

在系统正常运行和两种故障状态时的运行方式;The operation mode when the system is in normal operation and in two fault states;

系统正常运行时,Idc>0,中间支路串联正向的直流偏置电源,使Ib>Idc。流过二极管D1和D4的电流为(Ib+Idc)/2>0,流过二极管D2和D3的电流为(Ib-Idc)/2>0,因此4个二极管均正向导通,限流器被旁路,直流线路上的电流不会流过中间支路,该支路电流较小。;When the system is in normal operation, I dc >0, the intermediate branch is connected in series with a forward DC bias power supply, so that I b >I dc . The current through diodes D 1 and D 4 is (I b +I dc )/2>0, and the current through diodes D 2 and D 3 is (I b -I dc )/2>0, so 4 diodes Both are forward conducting, the current limiter is bypassed, the current on the DC line will not flow through the middle branch, and the current in this branch is small. ;

其中当直流配电网出现极间短路故障时,线路电流Idc增大,Ib<Idc,此时二极管D2和D3上的电流为(Ib-Idc)/2<0,所以此时只有二极管D1和D4导通,直流侧故障电流流经中间支路的限流电感,其幅值得以抑制。如图5所示,将直流偏置电源同全控型晶体管并联。单极接地故障情况下,G1信号控制晶体管导通,直流电源被短路,只有D1和D4正向导通,限流电感接入直流线路;Among them, when the inter-pole short-circuit fault occurs in the DC distribution network, the line current I dc increases, I b <I dc , and the currents on the diodes D 2 and D 3 at this time are (I b -I dc )/2<0, Therefore, only diodes D 1 and D 4 are turned on at this time, and the DC side fault current flows through the current-limiting inductance of the intermediate branch, and its amplitude can be suppressed. As shown in Figure 5, connect the DC bias power supply in parallel with the fully controlled transistor. In the case of unipolar grounding fault, the G 1 signal controls the transistor to be turned on, the DC power supply is short-circuited, only D 1 and D 4 are forwardly conducting, and the current limiting inductor is connected to the DC line;

如图2所示,本发明提供了一种适用于新型柔性限流器的控制方法,具体过程如下:As shown in Figure 2, the present invention provides a control method suitable for a novel flexible current limiter, and the specific process is as follows:

通过整流器提供的线性电流,限流电感的钳位电压被控制在稳定的数值。因此,限流电感的电压Ul被作为柔性限流器换流站的控制目标。双环控制的表达式如下:The clamping voltage of the current limiting inductor is controlled to a stable value by the linear current supplied by the rectifier. Therefore, the voltage Ul of the current limiting inductor is used as the control target of the flexible current limiter converter station. The expression for double loop control is as follows:

Figure 990811DEST_PATH_IMAGE002
(1);
Figure 990811DEST_PATH_IMAGE002
(1);

在式(1)中,K是放大增益,K vf 是反馈系数,u set i q2 为控制系统的输入量和扰动量;其中In formula (1), K is the amplification gain, K vf is the feedback coefficient, u set and i q2 are the input quantity and disturbance quantity of the control system; where

Figure 970268DEST_PATH_IMAGE004
(2)。
Figure 970268DEST_PATH_IMAGE004
(2).

根据保护判据,如果直流侧电压满足Udc≤0.8Udcn,则直流系统的故障可以被定义为极间短路故障。若电压满足下式,则故障能够被定义为单极接地故障According to the protection criterion, if the DC side voltage satisfies U dc ≤ 0.8U dcn , the fault of the DC system can be defined as an inter-pole short-circuit fault. The fault can be defined as a single-pole earth fault if the voltage satisfies the following equation

Figure DEST_PATH_IMAGE009
(3);
Figure DEST_PATH_IMAGE009
(3);

在不同的故障条件下,柔性限流器控制系统的输入量被设定为不同的数值Under different fault conditions, the input of the flexible current limiter control system is set to different values

Figure DEST_PATH_IMAGE010
(4);
Figure DEST_PATH_IMAGE010
(4);

其中,Udcn是直流系统的额定电压,U+ dc、U- dc分别为直流侧正负极的电压,U+ dcn和U- dcn分别为正负极电压的额定值。m1,m2和m3是系统输入的控制系数且mi=0~1(i=1,2,3)。Among them, U dcn is the rated voltage of the DC system, U + dc , U - dc are the voltages of the positive and negative poles of the DC side, respectively, and U + dcn and U - dcn are the rated values of the positive and negative voltages, respectively. m 1 , m 2 and m 3 are control coefficients input by the system and m i =0∼1 (i=1, 2, 3).

故障时,针对不同故障位置,控制系数在区间内能够被人为改变。极间短路故障情况下,若m1数值较小,故障回路的放电压降依旧较大,故选择其最小值为0.5以避免产生过大的故障电流。单极接地故障时,系统的主要问题在于正负极电压不平衡,其不平衡度同m2、m3的数值大小呈负相关。因单极接地故障的危害较小,为保证故障情况下系统的平稳运行,以及延长可供故障检测的时间,选定m2、m3的最小值为0.6。故控制系数mi的选取区间为When a fault occurs, the control coefficient can be artificially changed within the interval for different fault locations. In the case of inter-pole short-circuit fault, if the value of m 1 is small, the discharge voltage drop of the fault circuit is still large, so the minimum value is selected to be 0.5 to avoid excessive fault current. When a single-pole ground fault occurs, the main problem of the system is that the positive and negative voltages are unbalanced, and the unbalance degree is negatively correlated with the values of m 2 and m 3 . Because the harm of single-pole grounding fault is small, in order to ensure the smooth operation of the system under fault conditions and prolong the time available for fault detection, the minimum value of m 2 and m 3 is selected to be 0.6. Therefore, the selection interval of the control coefficient m i is

Figure DEST_PATH_IMAGE012
(5);
Figure DEST_PATH_IMAGE012
(5);

通过改变控制系数mi的数值,能够灵活改变限流器提供的钳位电压,进而改变了故障回路的故障电压,最终实现故障电流的柔性控制。By changing the value of the control coefficient mi , the clamping voltage provided by the current limiter can be flexibly changed, thereby changing the fault voltage of the fault circuit, and finally realizing the flexible control of the fault current.

根据式(1)-(2),可以得到限流装置的控制框图。限流器能够实现从正常运行状态到故障限流状态的切换,并且由于桥型电路的作用,限流器的状态切换对系统的影响可以忽略。限流器在配电网中的安装位置和控制系统如图2所示,串联在直流电网中,并通过交流测对限流器电压进行整流控制。According to equations (1)-(2), the control block diagram of the current limiting device can be obtained. The current limiter can realize the switching from the normal operation state to the fault current limiting state, and due to the function of the bridge circuit, the influence of the state switching of the current limiter on the system can be ignored. The installation position and control system of the current limiter in the distribution network are shown in Figure 2. They are connected in series in the DC grid, and the voltage of the current limiter is rectified and controlled by the AC measurement.

图2(A)设定了正极接地故障和负极接地故障的控制系统输入值,分别为m2U+ dcn和m3U- dcn。图2(B)为系统判断单极接地故障和极间短路故障的过程。当正极电压或者负极电压数值低于0.8倍的额定值,则可认为系统出现单极接地故障,Uset=Uset1。若不满足上述单极接地的故障条件,则Uset=Uset2。图2(C)中包含两个状态,当直流侧电压满足极间短路故障判断条件时Uset2=m1Udcn。否则,限流器控制系统的输入为0,即限流电感的电压为0,系统处于正常运行状态。Figure 2(A) sets the control system input values for positive ground fault and negative ground fault, which are m 2 U + dcn and m 3 U - dcn , respectively. Figure 2(B) shows the process of the system judging the single-pole grounding fault and the inter-pole short-circuit fault. When the positive voltage or negative voltage value is lower than 0.8 times the rated value, it can be considered that the system has a single-pole grounding fault, U set =U set1 . If the above single-pole grounding fault condition is not met, then U set =U set2 . Fig. 2(C) contains two states, when the DC side voltage satisfies the fault judgment condition of inter-pole short circuit, U set2 =m 1 U dcn . Otherwise, the input of the current limiter control system is 0, that is, the voltage of the current limiting inductor is 0, and the system is in a normal operation state.

如图3所示,限流电感的钳位电压Ul通过控制系统的输入值来设定。不同情况下,电感电压可分别设置为如图所示的四个数值。整流器提供线性上升的电流来保持钳位电压的稳定,若限流电感饱和,电感电流的斜率无法维持,电感电压会发生变化,限流效果降低。故在柔性限流器的使用过程中,消除限流电感饱和的措施也应该被考虑。As shown in Figure 3, the clamping voltage U l of the current limiting inductor is set by the input value of the control system. In different cases, the inductor voltage can be set to four values as shown in the figure. The rectifier provides a linearly rising current to keep the clamping voltage stable. If the current limiting inductor is saturated, the slope of the inductor current cannot be maintained, the inductor voltage will change, and the current limiting effect will be reduced. Therefore, during the use of the flexible current limiter, measures to eliminate the saturation of the current limiting inductor should also be considered.

如图4所示,闭环铁芯可以用于防止限流电感饱和,N1绕组是限流电感,N2绕组是控制侧电感。限流电感饱和的具体表现为闭环铁芯内部的磁通饱和,二次侧的电感在闭环铁芯中产生反向的磁通以抑制限流电感磁通的增加,起到去饱和的作用。受控电压源作为二次侧电源,灵活调节反向磁通的大小,其控制量为I1,k为控制系数。As shown in Figure 4, the closed-loop iron core can be used to prevent the saturation of the current-limiting inductor, the N 1 winding is the current-limiting inductor, and the N 2 winding is the control-side inductor. The specific manifestation of current-limiting inductor saturation is that the magnetic flux inside the closed-loop iron core is saturated, and the inductance on the secondary side generates a reversed magnetic flux in the closed-loop iron core to suppress the increase in the magnetic flux of the current-limiting inductor and play a role in desaturation. The controlled voltage source is used as the secondary side power supply to flexibly adjust the magnitude of the reverse magnetic flux. The control quantity is I 1 , and k is the control coefficient.

铁芯的基本方程可表示为The basic equation of the iron core can be expressed as

Figure DEST_PATH_IMAGE014
(6);
Figure DEST_PATH_IMAGE014
(6);

其中,φ1是单匝线圈的磁通,Ψ1为总磁通,e1是N1绕组的电压。当铁芯磁通饱和时,电感L1饱和,其感电流不再线性上升,电压无法稳定控制在设定值Usetwhere φ1 is the magnetic flux of the single - turn coil, Ψ1 is the total magnetic flux, and e1 is the voltage of the N1 winding. When the iron core magnetic flux is saturated, the inductor L 1 is saturated, its inductive current no longer rises linearly, and the voltage cannot be stably controlled at the set value U set .

若磁感应强度和磁导率临近饱和,铁芯的反向磁通将增大,通过受控电压源的偏置,能够保证在故障期间,限流电感均处于不饱和状态。If the magnetic induction intensity and permeability are close to saturation, the reverse magnetic flux of the iron core will increase, and the bias of the controlled voltage source can ensure that the current-limiting inductance is not saturated during the fault period.

如图5所示,柔性限流器能够消除单极接地故障正负极电压的不平衡,也能降低极间短路故障的故障电流幅值。柔性限流器的操作过程可以分为四个阶段,分别为:正常运行阶段、故障限流阶段、铁芯饱和消除阶段以及恢复阶段。As shown in Figure 5, the flexible current limiter can eliminate the imbalance of the positive and negative voltages of the single-pole grounding fault, and can also reduce the fault current amplitude of the inter-pole short-circuit fault. The operation process of the flexible current limiter can be divided into four stages: normal operation stage, fault current limiting stage, iron core saturation elimination stage and recovery stage.

阶段(1):系统正常运行时,桥型电路的四个二极管均导通,直流线路电流不会流过限流支路,流经该支路的电流较小。如图5(1)所示,正常状态下,限流器不需要向电网取电,铁芯二次侧的受控源也不会动作,限流器不影响系统的正常运行。Stage (1): When the system is in normal operation, the four diodes of the bridge circuit are all turned on, the DC line current will not flow through the current-limiting branch, and the current flowing through this branch is small. As shown in Figure 5(1), under normal conditions, the current limiter does not need to take power from the grid, and the controlled source on the secondary side of the iron core will not operate, and the current limiter does not affect the normal operation of the system.

阶段(2):直流系统的短路故障可以分为接地短路故障和极间短路故障。故障期间,桥型电路中只有D1和D4两个二极管导通,故障电流的流通路径被切换到限流支路上。以正极接地故障为例,其故障回路如图5(2)中的①所示,限流电感在该阶段开始动作,未达到饱和状态,故受控电压源不会动作。限流电感的电压为Ul,且有Ul=m2U+ dcn,正极电压将上升至Ul,同时负极电压降低,消除了单极接地故障时正负极电压的不平衡。极间短路的故障回路如图5(2)中的②所示,此时限流电感电压Ul=m1Udcn,在故障回路中可作为一个大小可变的钳位电压,进而减小AC/DC换流站出口电容的放电电压。Stage (2): The short-circuit fault of the DC system can be divided into ground short-circuit fault and inter-pole short-circuit fault. During the fault, only two diodes D 1 and D 4 are turned on in the bridge circuit, and the flow path of the fault current is switched to the current-limiting branch. Taking the positive ground fault as an example, the fault loop is shown as ① in Figure 5(2). The current-limiting inductance starts to act at this stage and does not reach the saturation state, so the controlled voltage source will not act. The voltage of the current-limiting inductor is U l , and there is U l =m 2 U + dcn , the positive voltage will rise to U l , and the negative voltage will decrease at the same time, which eliminates the imbalance of positive and negative voltages during single-pole grounding faults. The fault circuit with short-circuit between poles is shown as ② in Figure 5(2). At this time, the current-limiting inductor voltage U l =m 1 U dcn can be used as a variable-sized clamping voltage in the fault circuit, thereby reducing the AC voltage. /DC converter station outlet capacitor discharge voltage.

阶段(3):在限流器作用一段时间之后,若故障还未切除,则需要通过铁芯二次侧的受控源来延长限流电感的有效限流时间。受控电流源的装设位置如图5(3)所示,二次侧电流在铁芯中产生反向磁通,消除电感的饱和状态。根据限流电感的饱和情况,受控源的电压能够自适应调整,维持限流电感的不饱和状态,保证限流器的可靠性。Stage (3): After the current limiter acts for a period of time, if the fault has not been removed, it is necessary to extend the effective current limiting time of the current limiting inductor through the controlled source on the secondary side of the iron core. The installation position of the controlled current source is shown in Figure 5(3). According to the saturation condition of the current limiting inductor, the voltage of the controlled source can be adjusted adaptively to maintain the unsaturated state of the current limiting inductor and ensure the reliability of the current limiter.

阶段(4):故障消失或者被清除时,桥型电路上的四个二极管恢复导通,限流器再次被旁路,其恢复状态的过程不影响正常状态下的系统。限流电感上的能量向电网释放,系统可以被分为主回路和能量释放回路,如图5(4)所示。在主回路中,直流系统的电压和电流恢复至额定值。在放电回路中,柔性限流器中的换流器转变为逆变状态,电感能量通过逆变器流向电网,降低能量的损耗。Stage (4): When the fault disappears or is cleared, the four diodes on the bridge circuit resume conduction, the current limiter is bypassed again, and the process of its recovery state does not affect the system in normal state. The energy on the current-limiting inductor is released to the grid, and the system can be divided into a main loop and an energy release loop, as shown in Figure 5(4). In the main circuit, the voltage and current of the DC system are restored to their rated values. In the discharge loop, the converter in the flexible current limiter is transformed into an inverter state, and the inductive energy flows to the grid through the inverter to reduce energy loss.

基于上述原理,柔性限流器能够通过在故障回路中增加反向的钳位电压来减小电容的放电电压。Based on the above principles, the flexible current limiter can reduce the discharge voltage of the capacitor by increasing the reverse clamping voltage in the fault loop.

如图6所示,As shown in Figure 6,

单极接地故障:Single pole ground fault:

限流器装设在换流站的出口,单极接地故障发生的时候,限流器作用于正极电容和故障点之间,如图6(1)所示。限流器能够提供一个稳定的钳位电压,故负极电压可表示为The current limiter is installed at the outlet of the converter station. When a single-pole ground fault occurs, the current limiter acts between the positive capacitor and the fault point, as shown in Figure 6(1). The current limiter can provide a stable clamping voltage, so the negative voltage can be expressed as

Figure DEST_PATH_IMAGE016
(7);
Figure DEST_PATH_IMAGE016
(7);

经柔性限流器的作用,负极电压随着正极电压的升高而减小。因此,如果此时限流电感电压设定合理,系统能够隔离单极接地故障点而正常运行,保证直流配电网供电的稳定性。With the action of the flexible current limiter, the negative electrode voltage decreases with the increase of the positive electrode voltage. Therefore, if the current-limiting inductor voltage is set reasonably at this time, the system can isolate the single-pole ground fault point and operate normally, ensuring the stability of the DC distribution network power supply.

极间短路故障:Interpole short circuit fault:

如图6(2)所示,因钳位电压的作用,电容的放电电压减小,可表示为As shown in Figure 6(2), the discharge voltage of the capacitor decreases due to the clamp voltage, which can be expressed as

Figure DEST_PATH_IMAGE018
(8);
Figure DEST_PATH_IMAGE018
(8);

其中,U dc为出口电容的等效放电电压。在电容的放电电压减小后,故障电流也将得到限制。因为Ul=Uset=m1Udcn,该数值通过改变m1的大小是能够灵活变化的。因此,电容等效放电电压也能够灵活变化,故障电流的柔性控制得以实现。Among them, U ' dc is the equivalent discharge voltage of the outlet capacitor. After the discharge voltage of the capacitor is reduced, the fault current will also be limited. Because U l =U set =m 1 U dcn , this value can be flexibly changed by changing the size of m 1 . Therefore, the equivalent discharge voltage of the capacitor can also be changed flexibly, and the flexible control of the fault current can be realized.

以上所述仅为本发明的较佳实施例,凡依本发明申请专利范围所做的均等变化与修饰,皆应属本发明的涵盖范围。The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (4)

1. A flexible current limiter which can be connected in series on a direct current circuit is characterized by comprising a bridge circuit, a current limiter and a current limiter voltage-controlled rectifying module, wherein the current limiter is arranged on a bridge arm of the bridge circuit; the bridge circuit comprises a first diode D1A second diode D2A third diode D3A fourth diode D4A current-limiting inductor L and a controllable DC bias power supply Ib(ii) a The first diode D1Cathode and controllable DC bias power supply IbNegative pole and second inductance L2The cathodes are respectively connected; the first diode D1Anode and third diode D3Connecting a cathode; the third diode D3Anode and one end of current-limiting inductor L and fourth diode D4The anodes are respectively connected; the fourth diode D4Cathode and second diode D2Connecting an anode; the current-limiting inductor L and the controllable DC bias power supply IbConnecting the positive electrodes;
the control method of the flexible current limiter is specifically
When the system runs normally, the bridge circuit bypasses the current limiter, and the running of the system is not influenced;
during a fault period, the bridge circuit is switched, the current limiter is connected into a system and provides variable clamping voltage for a fault loop, so that the voltage drop of an outlet capacitor of the AC/DC converter station is controlled, and overlarge fault current is restrained; the current limiter controls the clamping voltage of the current-limiting inductor to be a stable value through the linear current provided by the rectifier, so that the voltage of the current-limiting inductor L is controlledu l Is taken as a control target for the flexible current limiter converter station;
the expression for the dual loop control is as follows:
Figure DEST_PATH_IMAGE002
(1);
in the formula (1), the reaction mixture is,Kis the gain of the amplification and is,K vf is the coefficient of the feedback that is,u set andi q2 the input quantity and the disturbance quantity of the control system; wherein
Figure DEST_PATH_IMAGE004
(2)。
2. The flexible current limiter of claim 1, wherein the flexible current limiter comprises a closed-loop core with a controlled source for eliminating saturation of the current limiting inductor L, the core having a primary side as the current limiter and a secondary side as the controlled source.
3. The flexible current limiter according to claim 1, wherein the fault determination is specifically: according to the protection criterion, if the DC side voltage satisfiesU dc ≤0.8U dcn Then the fault of the dc system may be defined as an inter-electrode short fault;
if the voltage satisfies the following formula, the fault can be defined as a single pole ground fault
Figure DEST_PATH_IMAGE006
(3);
The input of the flexible current limiter control system is set to different values under different fault conditions
Figure DEST_PATH_IMAGE008
(4);
Wherein, UdcnIs the rated voltage of the direct current system,U + dc U - dc the voltages of the positive and negative electrodes on the direct current side respectively,U + dcn andU - dcn rated values of positive and negative voltages respectively;m 1 m 2 andm 3 is the control coefficient of the system input.
4. The flexible current limiter according to claim 1, wherein during the fault, the current limiter changes the clamping voltage provided by the current limiter by changing the value of the control coefficient according to different fault positions, so as to change the fault voltage of the fault loop, and finally realize flexible control of the fault current.
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