CN106053987A

CN106053987A - Multi-inverter microgrid quick island detection method

Info

Publication number: CN106053987A
Application number: CN201610414617.7A
Authority: CN
Inventors: 陈晓龙; 李永丽
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2016-06-13
Filing date: 2016-06-13
Publication date: 2016-10-26
Anticipated expiration: 2036-06-13
Also published as: CN106053987B

Abstract

The invention relates to a fast island detection method suitable for multi-inverter microgrids. The method is based on the real-time measurement of the voltage effective value V _PCC at the PCC and its frequency and load reactive power, by comparing the voltage measurement value with the Under normal circumstances, the rated value of voltage, frequency and its rated value of 50 Hz shall adopt the corresponding IBDG reactive power control strategy; when performing islanding judgment, the threshold value of voltage and frequency shall be preset first, and V _PCC and the threshold value of voltage For comparison, if the voltage threshold value is exceeded, it will be directly judged as an island state, and the current round of island detection will end; otherwise, the measured frequency f will be compared with the frequency threshold value, and if it exceeds the frequency threshold value, it will be judged as an island state . The invention does not have an island detection blind area, has universality, and is suitable for both the IBDG operating with the integral power factor and the IBDG operating with the non-integral power factor.

Description

A fast islanding detection method for multi-inverter microgrid

技术领域technical field

本发明属于电力系统微电网保护与控制领域，针对可能出现的微电网非计划孤岛问题，提出了一种适用于多逆变器型微电网的快速孤岛检测方法。The invention belongs to the field of micro-grid protection and control in power systems, and aims at the problem of unplanned islanding of micro-grids that may occur, and proposes a fast island detection method suitable for multi-inverter micro-grids.

背景技术Background technique

微电网非计划孤岛运行的发生具有偶然性和不确定性。当由于误操作、系统发生故障等原因引起公共耦合点或其上游断路器跳闸时，微电网内分布式电源可能无法及时检测到微电网已经与系统断开而继续保持运行。此时，微电网的非计划孤岛运行可能会给电力系统的安全稳定运行带来一系列问题，比如重合闸失败、备自投时间延长甚至失败、孤岛系统内电能质量恶化等，同时也会危害运维人员的人身安全。为了保证供电的可靠性和稳定性，美国电气电子工程师协会(IEEE)相关标准、我国国家标准以及电网公司企业标准要求分布式电源(DG)具有防孤岛保护的功能，即DG能够检测到非计划孤岛运行状态并退出运行。因此，非计划孤岛检测方法是防孤岛保护的核心技术。The occurrence of unplanned island operation of microgrid is accidental and uncertain. When the public coupling point or its upstream circuit breaker trips due to misoperation, system failure, etc., the distributed power generation in the microgrid may not be able to detect that the microgrid has been disconnected from the system in time and continue to operate. At this time, the unplanned island operation of the microgrid may bring a series of problems to the safe and stable operation of the power system, such as reclosing failure, extended or even failure of backup and automatic switching time, and deterioration of power quality in the island system. Personal safety of operation and maintenance personnel. In order to ensure the reliability and stability of power supply, the relevant standards of the Institute of Electrical and Electronics Engineers (IEEE), my country's national standards, and the enterprise standards of power grid companies require distributed power (DG) to have the function of anti-islanding protection, that is, DG can detect unplanned Island running state and out of running. Therefore, the unplanned islanding detection method is the core technology of anti-islanding protection.

现有的非计划孤岛检测方法包括开关状态监测法、被动检测法和主动检测法三大类：1)开关状态监测法是基于通讯技术将配电网侧断路器的开合状态发送给DG来判断微电网的运行模式，该方法不存在检测盲区，也不影响电能质量，但是该方法的实施较为复杂，经济性也较差，并且当通信网络发生故障时，该方法也随之失效；2)被动检测法通过检测电压、相位、频率及其变化率等基本电气量是否在允许变化范围之内来判定孤岛，该方法不会对系统电能质量造成影响，但是存在较大检测盲区，通常与主动检测法配合使用；3)主动检测法通常在DG的控制信号中注入扰动信号，并通过正反馈环节使得孤岛发生后相关电气量超出门槛值，从而判定孤岛，该方法能够减小甚至消除检测盲区，但同时也对电能质量造成了一定影响，并且由于多个DG中的扰动信号无法保证同步，也大大降低了孤岛检测的可靠性。The existing unplanned island detection methods include three categories: switch state monitoring method, passive detection method and active detection method: 1) The switch state monitoring method is based on communication technology to send the opening and closing state of the circuit breaker on the side of the distribution network to the DG. Judging the operation mode of the microgrid, this method does not have detection blind spots and does not affect power quality, but the implementation of this method is relatively complicated and the economy is poor, and when the communication network fails, the method will also fail; 2 ) The passive detection method judges the island by detecting whether the basic electrical quantities such as voltage, phase, frequency and its rate of change are within the allowable range of change. This method will not affect the power quality of the system, but there is a large detection blind spot, usually The active detection method is used together; 3) The active detection method usually injects a disturbance signal into the control signal of the DG, and through a positive feedback link, the relevant electrical quantity exceeds the threshold after the island occurs, thereby determining the island. This method can reduce or even eliminate the detection However, it also affects the power quality to a certain extent, and the synchronization of the disturbance signals in multiple DGs cannot be guaranteed, which greatly reduces the reliability of islanding detection.

目前，接入到低压电网中的DG主要是光伏发电系统、永磁直驱式风力发电系统以及微型燃气轮机发电系统等逆变型分布式电源(IBDG)。为快速实现微电网孤岛检测，申请人曾提出一种微电网孤岛检测方法^[1]，该方法通过对比并网点电压的有效值和额定值，采取相应的无功控制策略，当孤岛发生时，系统频率将超出门槛值，从而判定孤岛。对于多逆变器型微电网，当多个IBDG通过同一个PCC并网时，上述方法能够有效实现孤岛检测。然而，当多个IBDG的并网点位置不同时，尤其是不同并网点之间的距离较远并且两个并网点之间的线路上传输的功率较大的情况下，如果发生非计划孤岛，则不同位置IBDG的并网点电压值可能分别在额定电压值之上和之下，其无功扰动将相互抵消，无法保证孤岛检测的有效性。At present, the DGs connected to the low-voltage power grid are mainly inverter distributed power generation (IBDG) such as photovoltaic power generation systems, permanent magnet direct drive wind power generation systems, and micro gas turbine power generation systems. In order to quickly realize microgrid island detection, the applicant once proposed a microgrid island detection method ^[1] , which adopts a corresponding reactive power control strategy by comparing the effective value and rated value of the grid-connected point voltage. When islanding occurs, The system frequency will exceed the threshold value, thus determining islanding. For a multi-inverter microgrid, when multiple IBDGs are connected to the grid through the same PCC, the above method can effectively realize islanding detection. However, when the grid-connection points of multiple IBDGs are at different locations, especially when the distance between different grid-connection points is long and the power transmitted on the line between two grid-connection points is large, if unplanned islanding occurs, then The voltage values of grid-connected points of IBDG at different locations may be above and below the rated voltage, and their reactive power disturbances will cancel each other out, which cannot guarantee the effectiveness of islanding detection.

[1]李永丽，陈晓龙.一种微电网孤岛检测方法，授权发明专利，专利授权号：ZL201210319516.3，专利授权日：2014.10.15[1] Li Yongli, Chen Xiaolong. A microgrid island detection method, authorized invention patent, patent authorization number: ZL201210319516.3, patent authorization date: 2014.10.15

发明内容Contents of the invention

本发明的目的在于克服现有技术的不足，提供一种基于自适应无功扰动的、适用于多逆变器型微电网的快速孤岛检测方法。本发明的实质性特点是：1)不存在孤岛检测盲区；2)具有通用性，既适用于整功率因数运行的IBDG，也适用于非整功率因数运行的IBDG；3)根据PCC处电压及其频率的测量值和频率测量值的变化情况，自适应调整无功扰动斜率，减小了系统正常并网运行时IBDG的无功扰动，同时也缩短了孤岛检测时间；4)当微电网中含有多个IBDG时，无需通信就能保证无功扰动的同步性，从而保证孤岛检测的可靠性和有效性，简单易行。本发明的技术方案如下：The purpose of the present invention is to overcome the deficiencies of the prior art and provide a fast islanding detection method based on adaptive reactive power disturbance and applicable to multi-inverter microgrids. The substantive features of the present invention are: 1) There is no island detection blind area; 2) It is universal, applicable to both IBDGs operating with integral power factor and IBDGs operating with non-integer power factor; 3) According to the voltage at PCC and The measured value of its frequency and the change of the frequency measured value adaptively adjust the reactive power disturbance slope, which reduces the reactive power disturbance of the IBDG when the system is normally connected to the grid, and also shortens the islanding detection time; 4) when the microgrid When there are multiple IBDGs, the synchronization of reactive power disturbances can be guaranteed without communication, thereby ensuring the reliability and effectiveness of islanding detection, which is simple and easy to implement. Technical scheme of the present invention is as follows:

一种适用于多逆变器型微电网的快速孤岛检测方法，该方法在实时测量PCC处电压有效值V_PCC及其频率f和负载无功功率Q_load的基础上，通过比较电压测量值V_PCC与正常情况下电压额定值V_N、频率f与其额定值50Hz的大小情况，采取相应的IBDG无功控制策略：A fast islanding detection method suitable for multi-inverter microgrids, based on the real-time measurement of the voltage effective value V _PCC at the PCC and its frequency f and load reactive power Q _load , by comparing the voltage measurement V _{For PCC} and normal voltage rated value V _N , frequency f and its rated value of 50Hz, the corresponding IBDG reactive power control strategy is adopted:

1)当f大于或等于50Hz时，需根据V_PCC和V_N比较结果确定IBDG无功参考值；若V_PCC大于或等于V_N，则设置IBDG输出的无功功率为否则，设置IBDG输出的无功功率为Q_DG＝-k₁(f-49.2)+Q_Load；1) When f is greater than or equal to 50Hz, it is necessary to determine the IBDG reactive power reference value according to the comparison result of V _PCC and V _N ; if V _PCC is greater than or equal to V _N , set the reactive power output by the IBDG as Otherwise, set the reactive power of IBDG output as Q _DG =-k ₁ (f-49.2)+Q _Load ;

2)当f小于50Hz时，也根据V_PCC和V_N比较结果确定IBDG无功参考值；若V_PCC大于或等于V_N，则设置IBDG输出的无功功率为Q_DG＝-k₁(f-50.6)+Q_Load；否则，设置IBDG输出的无功功率为 2) When f is less than 50Hz, the reactive power reference value of IBDG is also determined according to the comparison result between V _PCC and V _N ; if V _PCC is greater than or equal to V _N , then set the reactive power output by IBDG as Q _DG =-k ₁ (f -50.6)+Q _Load ; otherwise, set the reactive power output by IBDG as

式中，k₁和k₂为无功控制策略中可调变量，其值均为正数；另外，根据f的大小自适应改变k₁取值，设置如下：In the formula, k ₁ and k ₂ are adjustable variables in the reactive power control strategy, and their values are both positive numbers; in addition, the value of k ₁ is adaptively changed according to the size of f, and the settings are as follows:

${k k}_{11} = = \{\begin{matrix} 0.01 0.01 {P P}_{D D. G G},, & | | f f - - 5050 | | \leq \leq 0.1 0.1 H h z z \\ 0.02 0.02 {P P}_{D D. G G},, & 0.1 0.1 H h z z < < | | f f - - 5050 | | \leq \leq 0.2 0.2 H h z z \\ 0.03 0.03 {P P}_{D D. G G},, & 0.2 0.2 H h z z < < | | f f - - 5050 | | \leq \leq 0.3 0.3 H h z z \\ 0.04 0.04 {P P}_{D D. G G},, & 0.3 0.3 H h z z < < | | f f - - 5050 | | \leq \leq 0.4 0.4 H h z z \\ 0.05 0.05 {P P}_{D D. G G},, & 0.4 0.4 H h z z < < | | f f - - 5050 | | \end{matrix}$

式中，P_DG为DG输出的有功功率，当系统频率f满足|f-50|>0.1Hz时，若在一定时间内频率没有超出频率门槛值，则k₁仍取为0.01P_DG；In the formula, P _DG is the active power output by DG. When the system frequency f satisfies |f-50|>0.1Hz, if the frequency does not exceed the frequency threshold within a certain period of time, then k ₁ is still taken as 0.01P _DG ;

在进行孤岛判断时，首先预设电压门槛值和频率门槛值，并将V_PCC与电压门槛值进行比较，若超出电压门槛值，则直接判定为孤岛状态，结束本轮的孤岛检测；否则，将所测得的频率f与频率门槛值进行比较，若超出频率门槛值，则判定为孤岛状态。When performing island judgment, first preset the voltage threshold and frequency threshold, and compare V _PCC with the voltage threshold. If the voltage threshold is exceeded, it will be directly judged as an island state, and the current round of island detection will end; otherwise, The measured frequency f is compared with the frequency threshold value, and if it exceeds the frequency threshold value, it is determined to be an island state.

为快速有效地实现多逆变器型微电网孤岛检测，本发明以不同位置IBDG测量值均相同的频率作为扰动方向的依据，提出自适应改变无功扰动斜率的快速孤岛检测方法。与现有技术相比，该方法所能产生的积极效果是：首先，本发明具有通用性，既适用于整功率因数运行的IBDG，也适用于为本地负载同时提供无功补偿的非整功率因数运行的IBDG；其次，本发明通过自适应改变无功扰动斜率，保证了正常运行时较小的无功扰动，减小了对电能质量的影响，缩短了检测时间，并且不存在孤岛检测盲区；再次，在微电网并网运行时，本发明根据系统电压状态进行无功补偿，能够改善并网点电压质量；最后，本发明适用于含有多个IBDG的微电网，各个IBDG以系统频率的大小作为改变无功扰动斜率的依据，在无需通信的前提下能够同时输出使得系统频率增大或减小的无功扰动，保证了孤岛检测的可靠性和有效性。In order to quickly and effectively realize the islanding detection of multi-inverter microgrids, the present invention uses the same frequency of IBDG measurement values at different positions as the basis for the disturbance direction, and proposes a fast islanding detection method that adaptively changes the reactive power disturbance slope. Compared with the prior art, the positive effects that this method can produce are: firstly, the present invention is versatile, not only applicable to IBDGs operating with integral power factor, but also applicable to non-integral power that provides reactive power compensation for local loads at the same time The IBDG with factor operation; secondly, the present invention ensures small reactive power disturbance during normal operation by adaptively changing the slope of reactive power disturbance, reduces the impact on power quality, shortens the detection time, and does not have an island detection blind zone ; Again, when the microgrid is connected to the grid, the present invention performs reactive power compensation according to the system voltage state, which can improve the voltage quality of the grid-connected point; finally, the present invention is applicable to a microgrid containing multiple IBDGs, and each IBDG is based on the size of the system frequency As the basis for changing the slope of the reactive power disturbance, the reactive power disturbance that increases or decreases the system frequency can be simultaneously output without communication, which ensures the reliability and effectiveness of the islanding detection.

附图说明Description of drawings

图1为标准孤岛测试系统主电路拓扑图，其中(a)为并网运行模式，(b)为孤岛运行模式；Figure 1 is the main circuit topology diagram of the standard island test system, where (a) is the grid-connected operation mode, and (b) is the island operation mode;

图2为IBDG的PQ解耦控制框图；Figure 2 is a block diagram of the PQ decoupling control of IBDG;

图3为负载的Q-f曲线(负载消耗的有功功率P_Load＝200kW，功率因数为0.9)；Fig. 3 is the Qf curve of load (active power P _Load =200kW of load consumption, power factor is 0.9);

图4为IBDG整功率因数运行时负载和IBDG的Q-f曲线(P_DG＝200kW、负载品质因数Q_f＝2.5)；Fig. 4 is the Qf curve of the load and IBDG when the IBDG is running at a full power factor (PDG = _200kW , load quality factor _Qf = 2.5);

图5为所提适用于多逆变器型微电网快速孤岛检测方法的流程图。Fig. 5 is a flow chart of the proposed fast islanding detection method suitable for multi-inverter microgrids.

具体实施方式detailed description

下面将结合实施例及参照附图对该发明的技术方案进行详细说明。The technical solution of the invention will be described in detail below in conjunction with the embodiments and with reference to the accompanying drawings.

本发明根据系统频率的大小自适应改变施加在IBDG上无功扰动的斜率，提供了一种适用于多逆变器型微电网的快速孤岛检测方法。该方法不存在孤岛检测盲区，能够减小正常运行时的无功扰动，从而减小了对电能质量的影响，同时适用于整功率因数运行和非整功率因数运行的IBDG，并且各个IBDG无需通信、仅通过本地信息就能保证无功扰动的同步性，从而保证了孤岛检测的可靠性和有效性。The invention adaptively changes the slope of the reactive power disturbance applied to the IBDG according to the magnitude of the system frequency, and provides a fast island detection method suitable for multi-inverter microgrids. This method has no island detection blind area, can reduce reactive power disturbance during normal operation, thereby reducing the impact on power quality, and is suitable for IBDGs operating with integral power factor and non-integer power factor, and each IBDG does not need to communicate 1. The synchronization of reactive power disturbance can be guaranteed only through local information, thereby ensuring the reliability and effectiveness of islanding detection.

1.针对IBDG的孤岛测试系统及PQ解耦控制策略1. Island test system and PQ decoupling control strategy for IBDG

按照运行方式的不同，分布式电源一般可以分为传统旋转机型DG和IBDG。其中，IBDG通过电力电子装置与电网并联，是目前DG并入配电网的主要形式，IEEE Std.929-2000和IEEE Std.1547-2003中规定的分布式电源和并网逆变器的标准孤岛测试系统如图1所示[1,2]。在并网运行模式下，IBDG通过公共耦合点(PCC)和配电网相连，同时为负荷提供功率，负荷消耗的有功和无功与负荷等效阻抗之间的关系式分别为：According to different operating modes, distributed power can generally be divided into traditional rotary models DG and IBDG. Among them, IBDG is connected in parallel with the power grid through power electronic devices, which is the main form of DG integrated into the distribution network at present. The standards for distributed power and grid-connected inverters stipulated in IEEE Std.929-2000 and IEEE Std.1547-2003 The island test system is shown in Figure 1 [1,2]. In the grid-connected operation mode, the IBDG is connected to the distribution network through the point of public coupling (PCC) and provides power to the load at the same time. The relationship between the active power and reactive power consumed by the load and the equivalent impedance of the load are respectively:

${P P}_{L L o o a a d d} = = {P P}_{D D. G G} + + {P P}_{G G r r i i d d} = = 33 \frac{{V V}_{P P C C C C}^{22}}{R R} - - - - - - ((11))$

${Q Q}_{L L o o a a d d} = = {Q Q}_{D D. G G} + + {Q Q}_{G G r r i i d d} = = 33 {V V}_{P P C C C C}^{22} ((\frac{11}{22 π π f f L L} - - 22 π π f f C C)) - - - - - - ((22))$

式中，V_PCC为PCC处的电压，f为PCC处电压的频率，P_Load和P_DG分别为负载消耗的有功功率和DG输出的有功功率，Q_Load和Q_DG分别为负载消耗的无功功率和DG输出的无功功率，R、L和C分别为等效负载的电阻、电感和电容值。当图1中所示开关打开时，IBDG和负荷形成孤岛，负荷所需电能完全由IBDG提供。当发生非计划孤岛时，若IBDG提供的功率等于或者接近负荷消耗所需要的功率，则PCC处电压和频率将在正常运行允许范围之内，被动检测法过压/欠压法(OVP/UVP)和过频/欠频法(OFP/UFP)将无法检测到非计划孤岛的发生，从而进入检测盲区。In the formula, V _PCC is the voltage at PCC, f is the frequency of voltage at PCC, P _Load and PDG are the active power consumed by the load and the active power output by _DG , respectively, Q _Load and Q _DG are the reactive power consumed by the load Power and reactive power output by DG, R, L and C are the resistance, inductance and capacitance of the equivalent load respectively. When the switch shown in Figure 1 is turned on, the IBDG and the load form an island, and the power required by the load is completely provided by the IBDG. When unplanned islanding occurs, if the power provided by the IBDG is equal to or close to the power consumed by the load, the voltage and frequency at the PCC will be within the allowable range for normal operation. The passive detection method (OVP/UVP) ) and the overfrequency/underfrequency method (OFP/UFP) will not be able to detect the occurrence of unplanned islanding, thus entering the detection blind zone.

基于瞬时功率理论，IBDG采用PQ解耦控制策略，从而可以通过借助IBDG的无功控制策略实现快速孤岛检测。PQ解耦控制策略的控制框图如图2所示，包括锁相环、功率外环和电流内环[3,4]。通过引入PCC处的三相电压，锁相环可以提供实现同步派克变换的电压相位角，并能够计算出PCC处电压的频率。在功率外环中，通过一组比例积分(PI)调节器，将有功和无功的参考值与实际功率之间的误差分别调制为逆变器输出电流的有功和无功分量的参考值。电流内环则通过前馈控制算法，实现对逆变器输出电流的有功和无功分量的解耦控制。逆变器输出的有功功率和无功功率的公式如下：Based on the instantaneous power theory, IBDG adopts the PQ decoupling control strategy, so that fast islanding detection can be realized by using the reactive power control strategy of IBDG. The control block diagram of the PQ decoupling control strategy is shown in Figure 2, including the phase-locked loop, power outer loop and current inner loop [3,4]. By introducing the three-phase voltage at PCC, the phase-locked loop can provide the voltage phase angle to realize the synchronous Parker transformation, and can calculate the frequency of the voltage at PCC. In the power outer loop, through a set of proportional-integral (PI) regulators, the errors between the reference values of active and reactive power and the actual power are modulated into the reference values of the active and reactive components of the inverter output current, respectively. The current inner loop realizes the decoupling control of the active and reactive components of the inverter output current through the feedforward control algorithm. The formulas of active power and reactive power output by the inverter are as follows:

${P P}_{D D. G G} = = \frac{33}{22} {u u}_{d d} {i i}_{d d} - - - - - - ((33))$

${Q Q}_{D D. G G} = = \frac{33}{22} {u u}_{d d} {i i}_{q q} - - - - - - ((44))$

式中，i_d和i_q分别为DG输出电流的有功和无功分量，u_d为并网点电压的d轴分量。由上述两个公式可知，通过对输出电流的有功和无功分量的调节，可以实现对其有功和无功的独立控制，并达到所设定的功率参考值P_ref和Q_ref[4,5]。In the formula, i _d and i _q are the active and reactive components of the DG output current, respectively, and u _d is the d-axis component of the grid-connected point voltage. From the above two formulas, it can be seen that by adjusting the active and reactive components of the output current, the independent control of active and reactive power can be realized, and the set power reference values _{Pre and Q ref} _can be achieved [4,5 ].

上述段落里所涉及到的参考文献的出处如下：The sources of the references mentioned in the above paragraphs are as follows:

[1]IEEE Standard 929-2000.IEEE Recommended Practice for UtilityInterface of Photovoltaic(PV)Systems，2000.[1] IEEE Standard 929-2000. IEEE Recommended Practice for Utility Interface of Photovoltaic (PV) Systems, 2000.

[2]IEEE Standard 1547-2003.IEEE Standard for InterconnectingDistributed Resources with Electric Power Systems，2003.[2] IEEE Standard 1547-2003. IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems, 2003.

[3]田小禾，光储混合系统的控制与保护：[硕士学位论文]，天津：天津大学，2011.[3] Tian Xiaohe, Control and Protection of Photovoltaic Storage Hybrid System: [Master's Dissertation], Tianjin: Tianjin University, 2011.

[4]Zeineldin H.H.A Q-f droop curve for facilitating islandingdetection of inverter-based distributed generation.IEEE Transactions on PowerElectronics,2009,24(3):665-673.[4] Zeineldin H.H.A Q-f droop curve for facilitating islanding detection of inverter-based distributed generation. IEEE Transactions on Power Electronics, 2009, 24(3): 665-673.

[5]Schauder C,Mehta H.Vector analysis and control of advanced staticVAR compensators.IEE Proceedings C–Generation,Transmission and Distribution,1993,15(3):299-306.[5] Schauder C, Mehta H. Vector analysis and control of advanced static VAR compensators. IEE Proceedings C-Generation, Transmission and Distribution, 1993, 15(3): 299-306.

2.适用于多逆变器型微电网的快速孤岛检测方法2. A fast islanding detection method for multi-inverter microgrids

基于PQ解耦控制的IBDG能够以整功率因数或者非整功率因数运行。通常情况下，IBDG输出无功的参考值Q_ref设定为零，即IBDG按照单位功率因数运行，以便最大限度提高逆变器的运行效率。然而，当PCC处负荷无功需求大或者无功波动时，并网处电压将受到严重影响。因此，通过IBDG对负载进行无功补偿，能够减少配电网向PCC处负荷提供的无功，提高了负荷的功率因数，同时降低了输送无功造成的电压降落以及传输损耗。The IBDG based on PQ decoupling control can operate with integral power factor or non-integral power factor. Normally, the reference value Q _ref of reactive power output by the IBDG is set to zero, that is, the IBDG operates according to the unit power factor, so as to maximize the operating efficiency of the inverter. However, when the reactive power demand of the load at the PCC is large or the reactive power fluctuates, the voltage at the grid-connected point will be seriously affected. Therefore, the reactive power compensation of the load through the IBDG can reduce the reactive power provided by the distribution network to the load at the PCC, improve the power factor of the load, and reduce the voltage drop and transmission loss caused by the transmission of reactive power.

当发生非计划孤岛时，无论IBDG按照整功率因数运行还是按照非整功率因数运行，若其提供的功率等于或者接近负荷消耗所需要的功率，则PCC处电压和频率将在正常运行允许范围之内，OVP/UVP和OFP/UFP均将无法检测到非计划孤岛的发生，从而进入检测盲区。另外，若IBDG对负载进行无功补偿，则减小了孤岛后无功的不匹配度，从而增大加了检测盲区。When an unplanned island occurs, regardless of whether the IBDG operates according to the integral power factor or non-integral power factor, if the power it provides is equal to or close to the power consumed by the load, the voltage and frequency at the PCC will be within the allowable range for normal operation Both OVP/UVP and OFP/UFP will not be able to detect the occurrence of unplanned islands, thus entering the detection blind zone. In addition, if the IBDG performs reactive power compensation on the load, the mismatch degree of reactive power behind the island is reduced, thereby increasing the detection blind area.

为实现孤岛检测，虽然主动式方法通过引入扰动能够减小甚至消除孤岛检测盲区，但是当其应用在含有多个IBDG的微电网中时，现有大部分主动式方法无法保证扰动的同步性，从而可能无法实现孤岛检测。因此，必须探索一种适用于含有多个IBDG微电网的快速孤岛检测方法，不仅对整功率因数和非整功率因数运行的IBDG具有通用性，能够消除检测盲区，在系统正常运行时引入尽量小的扰动，而且能够在不借助通信的前提下仅通过本地信息就能保证多个IBDG中扰动的同步性，从而保证其可靠性和有效性。In order to realize islanding detection, although the active method can reduce or even eliminate the blind area of island detection by introducing disturbances, when it is applied in a microgrid containing multiple IBDGs, most of the existing active methods cannot guarantee the synchronization of disturbances. Islanding detection may thus not be possible. Therefore, it is necessary to explore a fast islanding detection method suitable for microgrids containing multiple IBDGs. , and can ensure the synchronization of disturbances in multiple IBDGs only through local information without communication, so as to ensure its reliability and validity.

无论正常运行还是非计划孤岛发生，负荷消耗的无功满足式(2)，并且结合式(1)，可进一步整理为下式：Regardless of normal operation or unplanned islanding, the reactive power consumed by the load satisfies formula (2), and combined with formula (1), it can be further organized into the following formula:

${Q Q}_{L L o o a a d d} = = {P P}_{L L o o a a d d} R R ((\frac{11}{22 π π f f L L} - - 22 π π f f C C)) - - - - - - ((55))$

若系统频率为50Hz，RLC负载消耗的有功功率为200kW，并且负载的功率因数为0.9，则负载的无功功率与系统频率之间关系图(即负载的Q-f曲线)如图3所示。由图3可知，在系统正常运行的频率范围附近(49.3Hz～50.5Hz的正常运行范围及其附近)，负载无功与系统频率的关系图近似线性，并且负载无功随着频率的增大而减小。If the system frequency is 50Hz, the active power consumed by the RLC load is 200kW, and the power factor of the load is 0.9, the relationship between the reactive power of the load and the system frequency (that is, the Q-f curve of the load) is shown in Figure 3. It can be seen from Figure 3 that the relationship between load reactive power and system frequency is approximately linear near the normal operating frequency range of the system (49.3Hz-50.5Hz normal operating range and its vicinity), and the load reactive power increases with frequency And reduce.

在非计划孤岛发生后，对于整功率因数运行的IBDG，在没有无功扰动的情况下，系统的频率值将最终等于负载的谐振频率值。若此时IBDG和负载之间的有功匹配，则无功不匹配与频率偏移之间的关系满足下式：After the occurrence of unplanned islanding, for the IBDG operating at full power factor, the frequency value of the system will eventually be equal to the resonant frequency value of the load in the absence of reactive power disturbance. If the active power between the IBDG and the load matches at this time, the relationship between the reactive power mismatch and the frequency offset satisfies the following formula:

$\{\begin{matrix} Δ Δ Q Q = = \frac{33 {V V}_{P P C C C C}^{22}}{22 π π f f L L} ((11 - - \frac{{f f}^{22}}{{((f f + + Δ Δ f f))}^{22}})) \\ Δ Δ f f = = {f f}_{i i} - - f f \end{matrix} - - - - - - ((66))$

式中，f_i为孤岛发生后的系统频率。对于非整功率因数运行的IBDG，则有功和无功不匹配均能够引起频率偏移，其关系分别满足下式：In the formula, f _i is the system frequency after the islanding occurs. For the IBDG operating with non-integer power factor, the mismatch of active power and reactive power can cause frequency offset, and the relationship satisfies the following formulas respectively:

$\{\begin{matrix} Δ Δ P P = = - - \frac{{P P}_{D D. G G} ((11 + + 44 {π π}^{22} {LCf LC}^{22}))}{f f ((11 - - 44 {π π}^{22} {LCf LC}^{22}))} Δ Δ f f \\ Δ Δ Q Q = = \frac{{Q Q}_{D D. G G} ((11 + + 44 {π π}^{22} {LCf LC}^{22}))}{f f ((11 - - 44 {π π}^{22} {LCf LC}^{22}))} Δ Δ f f \end{matrix} - - - - - - ((77))$

由式(7)可知，非计划孤岛发生后，若IBDG提供的有功和无功分别同时大于或同时小于负载所需有功和无功时，有功和无功不匹配将引起频率朝着不同方向变化，从而降低了孤岛检测速度，甚至进入孤岛检测盲区。因此，IBDG所采取的无功控制策略应尽量使得有功和无功不匹配同时引起频率增大或减小，从而实现快速孤岛检测。It can be seen from formula (7) that after the occurrence of unplanned islanding, if the active power and reactive power provided by IBDG are greater than or less than the active power and reactive power required by the load at the same time, the mismatch between active power and reactive power will cause the frequency to change in different directions , thus reducing the speed of island detection, and even entering the blind area of island detection. Therefore, the reactive power control strategy adopted by IBDG should try to make the mismatch between active power and reactive power cause the frequency to increase or decrease at the same time, so as to realize fast islanding detection.

为消除孤岛检测盲区，无功不匹配需要在频率允许范围内恒存在，即IBDG的Q-f曲线和负载的Q-f曲线之间在频率允许范围之内存在偏差。另外，无论系统正常运行还是发生非计划孤岛，不同位置的IBDG测量到的系统频率是相同的。因此，在不借助通信的前提下，为保证不同位置的IBDG仅根据本地信息就能保证无功扰动的同步性，则需要以系统频率值作为扰动判据。综上，IBDG的无功控制策略设计为：In order to eliminate the blind zone of island detection, reactive power mismatch needs to exist within the allowable frequency range, that is, there is a deviation between the Q-f curve of IBDG and the Q-f curve of the load within the allowable frequency range. In addition, the system frequency measured by the IBDG at different locations is the same regardless of whether the system is operating normally or unplanned islanding occurs. Therefore, under the premise of not relying on communication, in order to ensure the synchronization of reactive power disturbances between IBDGs in different locations only based on local information, it is necessary to use the system frequency value as the disturbance criterion. In summary, the reactive power control strategy of IBDG is designed as:

a.当PCC处电压的频率f大于或等于50Hz时a. When the frequency f of the voltage at the PCC is greater than or equal to 50Hz

Q_DG＝-k₁(f-49.2)+Q_Load (8)Q _DG ＝-k ₁ (f-49.2)+Q _Load (8)

b.当PCC处电压的频率f小于50Hz时b. When the frequency f of the voltage at PCC is less than 50Hz

Q_DG＝-k₁(f-50.6)+Q_Load (9)Q _DG ＝-k ₁ (f-50.6)+Q _Load (9)

式中，k₁为无功控制策略中可调变量，其值为正数。另外，k₁能够根据f的大小自适应改变取值，具体设置如下：In the formula, k ₁ is the adjustable variable in the reactive power control strategy, and its value is a positive number. In addition, k ₁ can adaptively change the value according to the size of f, and the specific settings are as follows:

${k k}_{11} = = \{\begin{matrix} 0.01 0.01 {P P}_{D D. G G},, & | | f f - - 5050 | | \leq \leq 0.1 0.1 H h z z \\ 0.02 0.02 {P P}_{D D. G G},, & 0.1 0.1 H h z z < < | | f f - - 5050 | | \leq \leq 0.2 0.2 H h z z \\ 0.03 0.03 {P P}_{D D. G G},, & 0.2 0.2 H h z z < < | | f f - - 5050 | | \leq \leq 0.3 0.3 H h z z \\ 0.04 0.04 {P P}_{D D. G G},, & 0.3 0.3 H h z z < < | | f f - - 5050 | | \leq \leq 0.4 0.4 H h z z \\ 0.05 0.05 {P P}_{D D. G G},, & 0.4 0.4 H h z z < < | | f f - - 5050 | | \end{matrix} - - - - - - ((1010))$

式中，P_DG为DG输出的有功功率。k₁的自适应变化，能够加快孤岛检测速度。另外，需要说明的是，当系统频率f满足|f-50|>0.1Hz时，若在1s内频率没有超出门槛值，则k₁仍取为0.01P_DG，这一设置能够避免系统发生短时扰动时无功扰动过大，从而保证系统的安全稳定运行。In the formula, P _DG is the active power output by DG. The adaptive change of k ₁ can speed up the islanding detection speed. In addition, it should be noted that when the system frequency f satisfies |f-50|>0.1Hz, if the frequency does not exceed the threshold within 1s, then k ₁ is still taken as 0.01P _DG . The reactive power disturbance is too large during the time disturbance, so as to ensure the safe and stable operation of the system.

根据式(7)分析可知，若有功和无功不匹配引起的频率偏移方向一致，则能够进一步提高孤岛检测速度。另外，在并网情况下，当PCC处电压偏高时，若IBDG发出的无功小于负载无功，则配电网向负载提供无功，能够使得PCC处电压降低；当PCC处电压偏低时，若IBDG发出的无功大于负载无功，则向配电网输入无功，从而使得PCC处电压恢复。即在并网情况下，IBDG的无功控制策略能够使得IBDG等效于无功补偿装置，改善PCC处电压质量。本发明所提IBDG无功控制策略的首要目标是实现含多个IBDG微电网的快速孤岛检测，在实现该目标的基础上可以兼顾电压质量调节功能，并将前述无功控制策略进一步改进如下：According to the analysis of formula (7), it can be seen that if the frequency offset direction caused by the mismatch of active power and reactive power is consistent, the islanding detection speed can be further improved. In addition, in the case of grid connection, when the voltage at PCC is high, if the reactive power generated by IBDG is less than the reactive power of the load, the distribution network will provide reactive power to the load, which can reduce the voltage at PCC; when the voltage at PCC is low , if the reactive power generated by the IBDG is greater than the reactive power of the load, the reactive power will be input to the distribution network, so that the voltage at the PCC will recover. That is, in the case of grid connection, the reactive power control strategy of the IBDG can make the IBDG equivalent to a reactive power compensation device and improve the voltage quality at the PCC. The primary goal of the IBDG reactive power control strategy proposed in the present invention is to realize rapid island detection with multiple IBDG microgrids. On the basis of realizing this goal, the voltage quality adjustment function can be taken into account, and the aforementioned reactive power control strategy is further improved as follows:

a.当PCC处电压的频率f大于或等于50Hz，并且电压V_PCC大于或等于V_N时a. When the frequency f of the voltage at PCC is greater than or equal to 50Hz, and the voltage V _PCC is greater than or equal to V _N

${Q Q}_{D D. G G} = = - - (({k k}_{11} + + ((\frac{{V V}_{P P C C C C} - - {V V}_{N N}}{{V V}_{N N}})) \times \times {k k}_{22})) ((f f - - 49.2 49.2)) + + {Q Q}_{L L o o a a d d} - - - - - - ((1111))$

b.当PCC处电压的频率f大于或等于50Hz，并且电压V_PCC小于V_N时b. When the frequency f of the voltage at PCC is greater than or equal to 50Hz, and the voltage V _PCC is less than V _N

Q_DG＝-k₁(f-49.2)+Q_Load (12)Q _DG ＝-k ₁ (f-49.2)+Q _Load (12)

c.当PCC处电压的频率f小于50Hz，并且电压V_PCC大于或等于V_N时c. When the frequency f of the voltage at PCC is less than 50Hz, and the voltage V _PCC is greater than or equal to V _N

Q_DG＝-k₁(f-50.6)+Q_Load (13)Q _DG ＝-k ₁ (f-50.6)+Q _Load (13)

d.当PCC处电压的频率f小于50Hz，并且电压V_PCC小于V_N时d. When the frequency f of the voltage at PCC is less than 50Hz, and the voltage V _PCC is less than V _N

${Q Q}_{D D. G G} = = - - (({k k}_{11} + + ((\frac{{V V}_{N N} - - {V V}_{P P C C C C}}{{V V}_{N N}})) \times \times {k k}_{22})) ((f f - - 50.6 50.6)) + + {Q Q}_{L L o o a a d d} - - - - - - ((1414))$

按照上述无功控制策略，不仅能够在并网情况下通过动态无功补偿实现动态改善PCC处电压质量，而且孤岛发生时有功的不匹配能够进一步加大无功的不匹配，从而进一步提高孤岛检测速度。According to the above reactive power control strategy, not only can dynamically improve the voltage quality at the PCC through dynamic reactive power compensation in the case of grid connection, but also the mismatch of active power when islanding occurs can further increase the mismatch of reactive power, thereby further improving islanding detection. speed.

非计划孤岛发生后，IBDG与负载之间有功的不匹配也会引起PCC处电压的变化，OVP/UVP法虽然存在盲区，但是当有功的不匹配程度足够大时，能够直接判断孤岛发生。因此，综合上述IBDG无功控制策略及OVP/UVP法、OFP/UFP法，形成如图5所示的不依赖通信的、适用于多逆变器型微电网的快速孤岛检测方法。该方案的具体步骤为：After unplanned islanding occurs, the active power mismatch between the IBDG and the load will also cause voltage changes at the PCC. Although there is a blind zone in the OVP/UVP method, when the active power mismatch is large enough, the islanding can be directly judged. Therefore, combining the above-mentioned IBDG reactive power control strategy, OVP/UVP method, and OFP/UFP method, a fast island detection method that does not rely on communication and is suitable for multi-inverter microgrids is formed as shown in Figure 5. The specific steps of the program are:

第一步：实时测量PCC处电压有效值V_PCC、频率f及负载无功Q_load。Step 1: Measure the effective value V _{PCC of the voltage at the PCC} , the frequency f and the reactive power Q _load of the load in real time.

第二步：将V_PCC和f与被动检测法OVP/UVP和OFP/UFP法中的电压和频率门槛值进行比较。若超出门槛值，则直接判定为孤岛状态；否则，转入下一步。Step 2: Compare V _PCC and f with the voltage and frequency thresholds in the passive detection methods OVP/UVP and OFP/UFP methods. If it exceeds the threshold, it is directly judged as an island state; otherwise, go to the next step.

第三步：根据V_PCC和f的值设置IBDG无功参考值，并转入第一步。The third step: Set the IBDG reactive power reference value according to the value of V _PCC and f, and turn to the first step.

需要说明的是，上述电压和频率门槛值可以参照被动检测法OVP/UVP和OFP/UFP法中的门槛值进行设定。It should be noted that the voltage and frequency thresholds above can be set with reference to the thresholds in the passive detection method OVP/UVP and OFP/UFP methods.

上述适用于多逆变器型微电网的快速孤岛检测方法，根据系统频率值自适应改变无功扰动斜率，减小了系统正常运行时的无功扰动量。该方法能够保证在正常频率运行范围内恒存在无功不匹配，因此不存在检测盲区。另外，不同位置的IBDG能够检测到相同的系统频率，在不依赖通信的前提下就能够保证扰动的同步性，从而保证了检测方法的可靠性和有效性。同时，本发明具有通用性，既适用于整功率因数运行的IBDG，也适用于为本地负荷提供无功补偿的IBDG。本发明也具有一定的电压质量调节能力。The above fast islanding detection method applicable to multi-inverter microgrid adaptively changes the slope of reactive power disturbance according to the system frequency value, reducing the amount of reactive power disturbance during normal operation of the system. This method can ensure that there is always a reactive power mismatch in the normal frequency operating range, so there is no detection blind zone. In addition, IBDGs at different locations can detect the same system frequency, and the synchronization of disturbances can be guaranteed without relying on communication, thus ensuring the reliability and effectiveness of the detection method. At the same time, the present invention has universality, and is applicable not only to IBDGs operating with integral power factor, but also to IBDGs providing reactive power compensation for local loads. The invention also has a certain voltage quality regulation capability.

以上内容仅为本发明的实施例，其目的并非用于对本发明所提出的系统及方法的限制，本发明的保护范围以权利要求为准。在不脱离本发明的精神和范围的情况下，本领域技术人员在不偏离本发明的范围和精神的情况下，对其进行的关于形式和细节的种种显而易见的修改或变化均应落在本发明的保护范围之内。The above content is only an embodiment of the present invention, and its purpose is not to limit the system and method proposed by the present invention. The scope of protection of the present invention is subject to the claims. Without departing from the spirit and scope of the invention, various obvious modifications or changes in form and details made by those skilled in the art without departing from the scope and spirit of the invention shall fall within the scope of this invention. within the scope of protection of the invention.

Claims

1. being applicable to a quick island detection method for multi-inverter type micro-capacitance sensor, the method measures voltage at PCC in real time Virtual value V_PCCAnd frequency f and load reactive power Q_loadOn the basis of, by comparison voltage measurement value V_PCCWith normal condition Lower voltage rating V_N, the size cases of frequency f and its rated value 50Hz, take the idle control strategy of corresponding IBDG:

1) when f is more than or equal to 50Hz, need to be according to V_PCCAnd V_NComparative result determines the idle reference value of IBDG；If V_PCCMore than or Equal to V_N, then the reactive power arranging IBDG output isOtherwise, arrange The reactive power of IBDG output is Q_DG=-k₁(f-49.2)+Q_Load；

2) when f is less than 50Hz, also according to V_PCCAnd V_NComparative result determines the idle reference value of IBDG；If V_PCCMore than or equal to V_N, The reactive power then arranging IBDG output is Q_DG=-k₁(f-50.6)+Q_Load；Otherwise, the reactive power arranging IBDG output is

In formula, k₁And k₂For regulated variable in idle control strategy, its value is positive number；It addition, change according to the size adaptation of f Become k₁Value, is provided that

k_{1} = \{\begin{matrix} 0.01 P_{D G}, & | f - 50 | \leq 0.1 H z \\ 0.02 P_{D G}, & 0.1 H z < | f - 50 | \leq 0.2 H z \\ 0.03 P_{D G}, & 0.2 H z < | f - 50 | \leq 0.3 H z \\ 0.04 P_{D G}, & 0.3 H z < | f - 50 | \leq 0.4 H z \\ 0.05 P_{D G}, & 0.4 H z < | f - 50 | \end{matrix}

In formula, P_DGThe active power exported for DG, when system frequency f meets | f-50 | > 0.1Hz, if frequency within a certain period of time Rate without departing from frequency threshold value, then k₁Still it is taken as 0.01P_DG；

When carrying out isolated island and judging, first predeterminated voltage threshold value and frequency threshold value, and by V_PCCCompare with voltage threshold value Relatively, if beyond voltage threshold value, the most directly it is judged to island state, terminates the isolated island detection of epicycle；Otherwise, by measured frequency Rate f compares with frequency threshold value, if beyond frequency threshold value, being then judged to island state.