CN110311375B - A control method for transient stability of microgrid with multiple virtual synchronous machines - Google Patents

A control method for transient stability of microgrid with multiple virtual synchronous machines Download PDF

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CN110311375B
CN110311375B CN201910687024.1A CN201910687024A CN110311375B CN 110311375 B CN110311375 B CN 110311375B CN 201910687024 A CN201910687024 A CN 201910687024A CN 110311375 B CN110311375 B CN 110311375B
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马大中
李林娟
刘丽月
王睿
胡旌伟
孙秋野
林森
安恩慧
李宇阳
程科
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Northeastern University China
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    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract

本发明公开一种含多虚拟同步机的微电网暂态稳定性控制方法，属于微电网暂态稳定性分析与控制技术领域。该方法充分考虑了虚拟惯量、虚拟阻尼、虚拟调速器下垂系数和无功控制环下垂系数，构建了含有多台虚拟同步机并联运行的微电网的能量函数模型，基于能量函数来分析判断系统的稳定性。并采用基于能量函数的自适应控制方法，对VSG中虚拟惯量、虚拟阻尼、虚拟调速器下垂系数和无功控制环下垂系数分别进行自适应实时调整，减小系统故障后的系统能量，增大系统的吸引域，减缓了系统能量达到临界能量的进程，为故障切除争取了有效时间，提高系统的暂态稳定性。

Figure 201910687024

The invention discloses a micro-grid transient stability control method with multiple virtual synchronous machines, belonging to the technical field of micro-grid transient stability analysis and control. This method fully considers the virtual inertia, virtual damping, virtual governor droop coefficient and reactive power control loop droop coefficient, constructs an energy function model of a microgrid with multiple virtual synchronous machines running in parallel, and analyzes and judges the system based on the energy function stability. And the self-adaptive control method based on energy function is adopted to adjust the virtual inertia, virtual damping, virtual governor droop coefficient and reactive control loop droop coefficient in VSG respectively in real time, so as to reduce the system energy after system failure and increase The attraction domain of the large system slows down the process of the system energy reaching the critical energy, buys effective time for fault removal, and improves the transient stability of the system.

Figure 201910687024

Description

一种含多虚拟同步机的微电网暂态稳定性控制方法A control method for transient stability of microgrid with multiple virtual synchronous machines

技术领域technical field

本发明涉及微电网暂态稳定性分析与控制技术领域，尤其涉及一种含多虚拟同步机的微电网暂态稳定性控制方法。The invention relates to the technical field of micro-grid transient stability analysis and control, in particular to a micro-grid transient stability control method with multiple virtual synchronous machines.

背景技术Background technique

近些年来，化石能源的枯竭和环境危机的加剧促进了分布式发电技术迅速发展。作为分布式电源(DG)、储能设备、电力电子变换器和负载等组成的系统，微电网在现代电力网络中越发普及。虚拟同步机控制策略(VSG)通过在电力电子变换器的控制环节中引入类似于传统同步发电机SG的机电暂态方程，分布式电源不仅能够模拟SG的有功调频、无功调压特性等运行外特性，还具有惯量特性和阻尼特性等动态特性。当微电网或大电网受到扰动或发生故障时，VSG可以有效地进行频率和电压调节，维持系统的稳定性。此外在其有功控制环(APCM)中的虚拟惯量、虚拟阻尼系数和VG中的下垂系数以及无功控制环(QPCM)中的下垂系数都可以根据实际需要灵活调整，以改善系统的稳定性，而传统SG的相应参数都是固定的。In recent years, the depletion of fossil energy and the intensification of the environmental crisis have promoted the rapid development of distributed power generation technology. As a system composed of distributed generation (DG), energy storage devices, power electronic converters and loads, microgrids are becoming more and more popular in modern power networks. The virtual synchronous machine control strategy (VSG) introduces the electromechanical transient equation similar to the traditional synchronous generator SG in the control link of the power electronic converter, and the distributed power supply can not only simulate the operation of the SG's active power frequency modulation and reactive power voltage regulation characteristics It also has dynamic characteristics such as inertia characteristics and damping characteristics. When the microgrid or large grid is disturbed or fails, the VSG can effectively regulate the frequency and voltage to maintain the stability of the system. In addition, the virtual inertia, virtual damping coefficient in the active power control loop (APCM), the droop coefficient in the VG and the droop coefficient in the reactive power control loop (QPCM) can be flexibly adjusted according to actual needs to improve the stability of the system. The corresponding parameters of the traditional SG are all fixed.

现有的含VSG微电网的暂态稳定性分析基本都是根据系统发生扰动后的频率变化率和频率变化量这两个指标进行分析，暂态稳定性控制基本是通过调整虚拟惯量或者虚拟阻尼这两个参数，改善系统频率和有功功率输出。虽方便直接，但分析方法较为单一，对于电压骤降，短路等故障情况的分析略显不足，而且仅靠频率无法解释系统的变化机理、反应变化本质。对于VSG而言，除了虚拟惯量和阻尼系数，VG中的下垂系数以及QPCM的下垂系数也可以影响其暂态稳定性。另外，基于频率的暂态稳定性分析需要时域仿真验证VSG对微电网暂态稳定性的作用，难以判断系统的稳定裕度，无法定量衡量系统受扰程度，而且当微电网中含有多台VSG并联运行时，不同VSG之间的频率偏差也容易影响分析的准确性。The existing transient stability analysis of the VSG microgrid is basically based on the frequency change rate and the frequency change amount after the system is disturbed. The transient stability control is basically by adjusting the virtual inertia or virtual damping. These two parameters improve system frequency and active power output. Although it is convenient and direct, the analysis method is relatively simple, and the analysis of fault conditions such as voltage sags and short circuits is slightly insufficient, and frequency alone cannot explain the change mechanism of the system and the nature of response changes. For VSG, in addition to the virtual inertia and damping coefficient, the droop coefficient in VG and QPCM can also affect its transient stability. In addition, frequency-based transient stability analysis requires time-domain simulation to verify the effect of VSG on the transient stability of the microgrid. It is difficult to judge the stability margin of the system, and it is impossible to quantitatively measure the degree of system disturbance. When VSGs are running in parallel, the frequency deviation between different VSGs is also likely to affect the accuracy of the analysis.

发明内容Contents of the invention

针对上述现有技术的不足，本发明提供一种含多虚拟同步机的微电网暂态稳定性控制方法。Aiming at the deficiencies of the above-mentioned prior art, the present invention provides a method for controlling the transient stability of a microgrid with multiple virtual synchronous machines.

为解决上述技术问题，本发明所采取的技术方案是一种含多虚拟同步机的微电网暂态稳定性控制方法，其流程如图1所示，包括如下步骤：In order to solve the above-mentioned technical problems, the technical solution adopted by the present invention is a microgrid transient stability control method with multiple virtual synchronous machines, the process of which is shown in Figure 1, including the following steps:

步骤1：构建含多台VSG并联运行的并网微电网的功率平衡模型，该模型包括包括VSG等效输出功率模型、联络线路等效传输功率模型和并网微电网的功率平衡方程；Step 1: Construct a power balance model of a grid-connected microgrid with multiple VSGs running in parallel, which includes the equivalent output power model of the VSG, the equivalent transmission power model of the tie line, and the power balance equation of the grid-connected microgrid;

步骤1.1：构建VSG等效输出功率模型，其中包含参数虚拟调速器VG、虚拟惯量、虚拟阻尼系数，包含有功控制模块APCM和无功控制模块QPCM两个部分；Step 1.1: Construct the VSG equivalent output power model, which includes the parameters virtual governor VG, virtual inertia, and virtual damping coefficient, including two parts: active power control module APCM and reactive power control module QPCM;

步骤1.1.1：有功控制模块APCM由VG和虚拟机械转动模块两部分组成，分别模拟SG的调速器和转子的机械运动方程，具体如下：Step 1.1.1: The active power control module APCM is composed of VG and virtual mechanical rotation module, which respectively simulate the mechanical motion equations of the governor and rotor of SG, as follows:

Figure BDA0002146672940000021
Figure BDA0002146672940000021

其中，Pei、Prefi分别为微电网中第i台VSG(VSGi,i＝1,2,...,N)的输出有功功率和控制器设置的有功功率参考值；

Figure BDA0002146672940000022
分别为VSGi的虚拟转动惯量和虚拟阻尼系数，用于模拟SG的转子运动特性；ωn、ωi分别为VSGi的额定角速度和VSGi的虚拟转子角速度,ωni＝ωn-ωi代表两者之差；δni表示VSGi虚拟转子的相对位移角，同时也是QPCM中输出电压与额定电压的相角差；
Figure BDA0002146672940000023
和
Figure BDA0002146672940000024
表示VSGi中VG输出的虚拟机械功率和虚拟下垂系数。Among them, P ei and P refi are respectively the output active power of the i-th VSG (VSGi,i=1,2,...,N) in the microgrid and the active power reference value set by the controller;
Figure BDA0002146672940000022
are the virtual moment of inertia and virtual damping coefficient of VSGi , which are used to simulate the rotor motion characteristics of SG; The difference; δ ni represents the relative displacement angle of the VSGi virtual rotor, and is also the phase angle difference between the output voltage and the rated voltage in QPCM;
Figure BDA0002146672940000023
and
Figure BDA0002146672940000024
Indicates the virtual mechanical power and virtual droop coefficient of VG output in VSGi.

步骤1.1.2：无功控制模块QPCM，在于模拟VSG的无功-电压调节特性，具体如下：Step 1.1.2: The reactive power control module QPCM is to simulate the reactive power-voltage regulation characteristics of VSG, as follows:

Figure BDA0002146672940000025
Figure BDA0002146672940000025

其中，Qei，Qrefi分别为VSGi的输出无功功率和控制器设置的无功功率参考值；Ei、En分别代表VSGi输出的电压幅值和额定电压幅值；

Figure BDA0002146672940000026
为QPCM下垂系数。Among them, Q ei and Q refi are the output reactive power of VSGi and the reference value of reactive power set by the controller; E i and En represent the voltage amplitude and rated voltage amplitude of VSGi output respectively;
Figure BDA0002146672940000026
is the QPCM droop coefficient.

步骤1.2：构建联络线路等效传输功率模型：Step 1.2: Construct the equivalent transmission power model of the tie line:

Figure BDA0002146672940000027
Figure BDA0002146672940000027

其中，

Figure BDA0002146672940000028
分别代表微电网中VSGi与电网连接的等效有功和无功传输功率；
Figure BDA0002146672940000029
分别代表传输线路阻抗和感抗；in,
Figure BDA0002146672940000028
represent the equivalent active and reactive transmission power of VSGi connected to the grid in the microgrid, respectively;
Figure BDA0002146672940000029
represent the transmission line impedance and inductive reactance respectively;

步骤1.3：考虑系统负载情况，建立并网微电网的功率平衡方程：Step 1.3: Considering the system load, establish the power balance equation of the grid-connected microgrid:

Figure BDA0002146672940000031
Figure BDA0002146672940000031

其中，PLi、QLi分别代表微电网所连接负载的有功功率和无功功率；Among them, P Li and Q Li respectively represent the active power and reactive power of the load connected to the microgrid;

步骤2：利用首次积分法构建考虑VG、虚拟惯量、虚拟阻尼系数的多台VSG并联运行的并网微电网的李雅普诺夫能量函数，计算微电网系统中的总能量VTOT；Step 2: Use the first integral method to construct the Lyapunov energy function of the grid-connected microgrid with multiple VSGs running in parallel considering VG, virtual inertia, and virtual damping coefficient, and calculate the total energy V TOT in the microgrid system;

步骤2.1：构建考虑权重关系的动能总能量函数VKE：Step 2.1: Construct the kinetic energy total energy function V KE considering the weight relationship:

步骤2.1.1：设置各动能项的权重因子

Figure BDA0002146672940000032
其中Mki为动能能量函数的阈值，i＝1,2,3；Step 2.1.1: Set the weight factor of each kinetic energy item
Figure BDA0002146672940000032
Where M ki is the threshold value of the kinetic energy function, i=1,2,3;

步骤2.1.2：构建微电网中所有VSG的虚拟惯量模拟的虚拟转子加/减速所引起的动能，具体如下：Step 2.1.2: Construct the kinetic energy caused by the virtual rotor acceleration/deceleration simulated by the virtual inertia of all VSGs in the microgrid, as follows:

Figure BDA0002146672940000033
Figure BDA0002146672940000033

其中，Mk1为动能能量函数VKE1的阈值；Among them, M k1 is the threshold value of kinetic energy energy function V KE1 ;

步骤2.1.3：构建虚拟阻尼系数和虚拟调速器的下垂系数所消耗的系统动能函数，具体如下：Step 2.1.3: Construct the system kinetic energy function consumed by the virtual damping coefficient and the droop coefficient of the virtual governor, as follows:

Figure BDA0002146672940000034
Figure BDA0002146672940000034

其中，ts为故障发生时间，

Figure BDA0002146672940000035
表示故障后系统的稳定平衡点处的转动角频率，Mk2为动能能量函数VKE2的阈值；Among them, t s is the fault occurrence time,
Figure BDA0002146672940000035
Indicates the rotational angular frequency at the stable equilibrium point of the system after a fault, and M k2 is the threshold value of the kinetic energy function V KE2 ;

步骤2.1.4：构建进行频率和功率的一次调节时所消耗的动能，具体如下：Step 2.1.4: Construct the kinetic energy consumed by one adjustment of frequency and power, as follows:

Figure BDA0002146672940000036
Figure BDA0002146672940000036

其中，χ＝dω/dt，Mk3为动能能量函数VKE3的阈值；Wherein, χ=dω/dt, M k3 is the threshold value of kinetic energy energy function V KE3 ;

步骤2.1.5：根据步骤2.1.1-2.14构建动能总能量函数VKE：Step 2.1.5: Construct the total kinetic energy function V KE according to steps 2.1.1-2.14:

VKE＝(VKE1+VKE2+VKE3) (8)V KE ＝(V KE1 +V KE2 +V KE3 ) (8)

步骤2.2：构建考虑权重关系的势能能量函数VPE：Step 2.2: Construct the potential energy function V PE considering the weight relationship:

步骤2.2.1：设置不同势能项的权重因子

Figure BDA0002146672940000041
其中Mpi为势能能量函数的阈值，i＝1,2,3,4；Step 2.2.1: Set weight factors for different potential energy items
Figure BDA0002146672940000041
Where M pi is the threshold value of the potential energy function, i=1,2,3,4;

步骤2.2.2：构建微电网系统中所有VSG的有功参考功率和有功负载引起的势能能量函数，具体如下：Step 2.2.2: Construct the active reference power of all VSGs in the microgrid system and the potential energy function caused by the active load, as follows:

Figure BDA0002146672940000042
Figure BDA0002146672940000042

其中，Mp1为势能能量函数VPE1的阈值；Among them, M p1 is the threshold of potential energy function V PE1 ;

步骤2.2.3：构建VSG的无功参考功率和无功负载引起的势能能量函数，具体如下：Step 2.2.3: Construct the reactive reference power of the VSG and the potential energy function caused by the reactive load, as follows:

Figure BDA0002146672940000043
Figure BDA0002146672940000043

其中，

Figure BDA0002146672940000044
为故障后系统电压的幅值，Mp2为势能能量函数VPE2的阈值；in,
Figure BDA0002146672940000044
is the magnitude of the system voltage after the fault, and M p2 is the threshold of the potential energy function V PE2 ;

步骤2.2.4：构建VSG与电网之间联络线路上传输的有功功率所代表的势能能量函数，具体如下：Step 2.2.4: Construct the potential energy function represented by the active power transmitted on the connection line between the VSG and the grid, as follows:

Figure BDA0002146672940000045
Figure BDA0002146672940000045

其中，

Figure BDA0002146672940000046
Figure BDA0002146672940000047
为故障后系统电压的相角，Mp3为势能能量函数VPE3的阈值；in,
Figure BDA0002146672940000046
Figure BDA0002146672940000047
is the phase angle of the system voltage after the fault, M p3 is the threshold of the potential energy function V PE3 ;

步骤2.2.5：构建VSG与电网之间联络线路上传输的无功功率所代表的势能能量函数，具体如下：Step 2.2.5: Construct the potential energy function represented by the reactive power transmitted on the connection line between the VSG and the grid, as follows:

Figure BDA0002146672940000048
Figure BDA0002146672940000048

其中，Mp4为势能能量函数VPE4的阈值；Among them, M p4 is the threshold value of potential energy energy function V PE4 ;

步骤2.2.6：根据步骤2.2.1-2.2.5,构建势能总能量函数，具体如下：Step 2.2.6: According to steps 2.2.1-2.2.5, construct the potential energy total energy function, as follows:

VPE＝VPE1+VPE2+VPE3+VPE4 (13)V PE ＝V PE1 +V PE2 +V PE3 +V PE4 (13)

步骤2.3：计算并网微电网的总能量函数VTOT：Step 2.3: Calculate the total energy function V TOT of the grid-connected microgrid:

VTOT＝VPE+VKE。 (14)V TOT =V PE +V KE . (14)

步骤3：根据现场需求设置能量函数的阈值，判断系统的运行状态；Step 3: Set the threshold of the energy function according to the site requirements, and judge the operating status of the system;

Figure BDA0002146672940000051
Figure BDA0002146672940000051

其中，MAVE为系统稳定运行时能量函数的阈值，VTOT为微电网系统中的总能量。Among them, M AVE is the threshold value of the energy function when the system is running stably, and V TOT is the total energy in the microgrid system.

步骤4:若系统稳定运行，执行步骤2继续计算；Step 4: If the system runs stably, perform step 2 to continue the calculation;

步骤5：若系统发生故障，则采用主导不稳定平衡点法，计算系统的临界能量Vcr；Step 5: If the system fails, use the dominant unstable equilibrium point method to calculate the critical energy V cr of the system;

步骤5.1：计算系统故障轨线至故障清除时刻以及出口点，具体如下：Step 5.1: Calculate the system fault trajectory to the fault clearing time and exit point, as follows:

Figure BDA0002146672940000052
Figure BDA0002146672940000052

步骤5.2：以出口点为初值，采用Gear方法计算故障后梯度系统的最小梯度点，具体如下：Step 5.2: Take the exit point as the initial value, and use the Gear method to calculate the minimum gradient point of the gradient system after the fault, as follows:

Figure BDA0002146672940000053
Figure BDA0002146672940000053

其中，

Figure BDA0002146672940000054
为最小梯度点；in,
Figure BDA0002146672940000054
is the minimum gradient point;

步骤5.3：以最小梯度点

Figure BDA0002146672940000055
为初值，求解系统的功率平衡方程得到系统的稳定平衡点和主导不稳定平衡点，具体如下：Step 5.3: Take the minimum gradient point
Figure BDA0002146672940000055
As the initial value, solve the power balance equation of the system to obtain the stable equilibrium point and dominant unstable equilibrium point of the system, as follows:

Figure BDA0002146672940000056
Figure BDA0002146672940000056

步骤5.4：根据系统主导不稳定平衡点处的状态量，计算出微电网并网系统的临界能量Step 5.4: Calculate the critical energy of the microgrid grid-connected system according to the state quantity at the dominant unstable equilibrium point of the system

Figure BDA0002146672940000061
Figure BDA0002146672940000061

其中，

Figure BDA0002146672940000062
分别为系统故障后微电网中VSGi的稳定平衡点和不稳定平衡点；
Figure BDA0002146672940000063
分别为微电网稳定运行时VSGi的虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数；
Figure BDA0002146672940000064
分别表示故障后系统的稳定平衡点处的转动角频率，电压的相角和幅值，χ＝dω/dt，ts为故障发生时间。in,
Figure BDA0002146672940000062
are the stable equilibrium point and unstable equilibrium point of VSGi in the microgrid after system failure, respectively;
Figure BDA0002146672940000063
are the virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient of VSGi when the microgrid is in stable operation;
Figure BDA0002146672940000064
respectively represent the rotational angular frequency at the stable equilibrium point of the system after the fault, the phase angle and amplitude of the voltage, χ=dω/dt, and t s is the fault occurrence time.

步骤6：启动基于能量函数的VSG虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数自适应控制方法；Step 6: Start the adaptive control method of VSG virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient based on energy function;

步骤6.1：基于能量函数的VSG虚拟惯量自适应控制方法：Step 6.1: VSG virtual inertia adaptive control method based on energy function:

Figure BDA0002146672940000065
Figure BDA0002146672940000065

其中，

Figure BDA0002146672940000066
分别为微电网稳定运行时VSGi的虚拟惯量和虚拟惯量最大值，MAVE为总能量函数的阈值。in,
Figure BDA0002146672940000066
are the virtual inertia and the maximum value of the virtual inertia of VSGi when the microgrid is in stable operation, and MAVE is the threshold of the total energy function.

步骤6.2：基于能量函数的VSG虚拟阻尼系数的自适应控制方法：Step 6.2: Adaptive control method of VSG virtual damping coefficient based on energy function:

Figure BDA0002146672940000067
Figure BDA0002146672940000067

其中，

Figure BDA0002146672940000068
分别表示微电网稳定运行时VSGi的虚拟阻尼系数和虚拟阻尼系数最大值。in,
Figure BDA0002146672940000068
Respectively represent the virtual damping coefficient and the maximum value of the virtual damping coefficient of VSGi when the microgrid is running stably.

步骤6.3：基于能量函数设计VG下垂系数的自适应控制方法：Step 6.3: Design an adaptive control method for the VG droop coefficient based on the energy function:

Figure BDA0002146672940000071
Figure BDA0002146672940000071

其中，

Figure BDA0002146672940000072
分别代表微电网稳定运行时VSGi的VG下垂系数和VG下垂系数最小值。in,
Figure BDA0002146672940000072
Represent the VG droop coefficient and the minimum value of VG droop coefficient of VSGi when the microgrid runs stably, respectively.

步骤6.4：基于能量函数设计QPCM下垂系数的自适应控制方法：Step 6.4: Design the adaptive control method of QPCM droop coefficient based on the energy function:

Figure BDA0002146672940000073
Figure BDA0002146672940000073

式中，

Figure BDA0002146672940000074
分别代表微电网稳定运行时VSGi的QPCM下垂系数和QPCM下垂系数最大值。In the formula,
Figure BDA0002146672940000074
Represent the QPCM droop coefficient and the maximum value of QPCM droop coefficient of VSGi when the microgrid runs stably, respectively.

步骤7：判断故障是否清除；Step 7: Determine whether the fault is cleared;

步骤8：执行步骤2计算故障清除时刻，微电网系统中的总能量Vcl；Step 8: Perform step 2 to calculate the total energy V cl in the microgrid system at the moment of fault clearing;

步骤9：将故障清除时刻微电网系统中的总能量Vcl与临界能量Vcr作比较，分析判断微电网的稳定性。Step 9: Compare the total energy V cl in the microgrid system at the moment of fault clearing with the critical energy V cr to analyze and judge the stability of the microgrid.

Figure BDA0002146672940000075
Figure BDA0002146672940000075

采用上述技术方案所产生的有益效果在于：The beneficial effects produced by adopting the above-mentioned technical scheme are:

1、本发明中考虑了虚拟惯量、虚拟阻尼、虚拟调速器下垂系数和无功控制环下垂系数，构建了含有多台虚拟同步机并联运行的微电网的能量函数模型，不仅可以分析扰动对微电网系统的影响，也可以反映发生故障后系统能量的变化。1. In the present invention, virtual inertia, virtual damping, virtual governor droop coefficient and reactive power control loop droop coefficient are considered, and an energy function model of a microgrid with multiple virtual synchronous machines running in parallel is constructed, which can not only analyze the effect of disturbance on The impact of the microgrid system can also reflect the change of system energy after a fault occurs.

2、本发明中基于能量函数来分析判断系统的稳定性，系统发生故障时，系统能量的变化远远大于频率的变化，便于检测和计算，对故障的敏感度高，有利于在故障初期阶段进行及时有效的控制，降低故障对系统的损害，提高系统的暂态稳定性。2. In the present invention, the stability of the system is analyzed and judged based on the energy function. When the system breaks down, the change of the system energy is far greater than the change of the frequency, which is convenient for detection and calculation, and has high sensitivity to the fault, which is beneficial to the initial stage of the fault. Carry out timely and effective control, reduce the damage to the system caused by faults, and improve the transient stability of the system.

3、本发明中在多台虚拟同步机并联运行的微电网中首次采用基于能量函数的4个VSG参数自适应控制方法，根据VSG中虚拟惯量、虚拟阻尼、虚拟调速器下垂系数和无功控制环下垂系数对系统能量的影响，分别设计了此4个参数的自适应控制方法，通过VSG参数的实时自适应调整，减小系统故障后的系统能量，增大系统的吸引域，减缓了系统能量达到临界能量的进程，为故障切除争取了有效时间，提高系统的暂态稳定性。3. In the present invention, the self-adaptive control method of 4 VSG parameters based on the energy function is adopted for the first time in the microgrid with multiple virtual synchronous machines running in parallel. According to the virtual inertia, virtual damping, virtual governor droop coefficient and reactive power The influence of the droop coefficient of the control loop on the system energy, the adaptive control method of these four parameters is designed respectively, through the real-time adaptive adjustment of the VSG parameters, the system energy after the system failure is reduced, the attraction area of the system is increased, and the The process in which the system energy reaches the critical energy wins effective time for fault removal and improves the transient stability of the system.

4、本发明中利用故障后的暂态能量来分析含多台虚拟同步机并联运行的微电网暂态稳定性，不仅可以判断系统的暂态稳定性，还可以定量的衡量系统的稳定裕度。4. In the present invention, the transient energy after the fault is used to analyze the transient stability of the microgrid with multiple virtual synchronous machines running in parallel, which can not only judge the transient stability of the system, but also quantitatively measure the stability margin of the system .

附图说明Description of drawings

图1为本发明一种含多虚拟同步机的微电网暂态稳定性控制方法的流程图；Fig. 1 is a flow chart of a microgrid transient stability control method containing multiple virtual synchronous machines of the present invention;

图2为本发明实施例的系统结构示意图以及虚拟同步机的控制结构示意图；Fig. 2 is a schematic diagram of a system structure and a schematic diagram of a control structure of a virtual synchronous machine according to an embodiment of the present invention;

图3为本发明实施例的等效电路图；Fig. 3 is the equivalent circuit diagram of the embodiment of the present invention;

图4为本发明实施例的微电网系统能量变化图；Fig. 4 is the diagram of the energy change of the microgrid system according to the embodiment of the present invention;

图5为本发明实施例中VSG的虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数根据能量函数的自适应控制变化示意图；5 is a schematic diagram of the adaptive control changes of the virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient of the VSG according to the energy function in the embodiment of the present invention;

图6为本发明实施例的VSG的虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数的实际取值示意图。FIG. 6 is a schematic diagram of actual values of virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient of the VSG according to an embodiment of the present invention.

具体实施方式Detailed ways

下面结合附图和实施例，对本发明的具体实施方式作进一步详细描述。以下实施例用于说明本发明，但不用来限制本发明的范围。The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

本实施例以某含有三台虚拟同步机并联运行的并网微电网进行分析，实施例的系统结构示意图和VSG的控制框图如图2所示。三台VSG并联运行，给负载供电，并通过联络线路与电网相连，其等效电路图如图3所示，三台VSG的额定容量相同，有功额定功率均为6kW，无功额定功率均为1kVA，额定电压380V，额定角速度为314rad/s，VSG和电网共同给负载(20kW 4kVA)供能。In this embodiment, a grid-connected microgrid with three virtual synchronous machines operating in parallel is analyzed. The system structure diagram of the embodiment and the control block diagram of the VSG are shown in FIG. 2 . Three VSGs run in parallel to supply power to the load and connect to the power grid through the contact line. The equivalent circuit diagram is shown in Figure 3. The rated capacity of the three VSGs is the same, the rated active power is 6kW, and the rated reactive power is 1kVA. , the rated voltage is 380V, and the rated angular velocity is 314rad/s. The VSG and the grid jointly supply energy to the load (20kW 4kVA).

步骤1：构建含三台VSG并联运行的并网微电网的功率平衡模型，该模型包括包括VSG等效输出功率模型、联络线路等效传输功率模型和并网微电网的功率平衡方程；Step 1: Construct the power balance model of the grid-connected microgrid with three VSGs running in parallel, which includes the VSG equivalent output power model, the equivalent transmission power model of the tie line and the power balance equation of the grid-connected microgrid;

步骤1.1：构建VSG等效输出功率模型，其中包含参数虚拟调速器VG、虚拟惯量、虚拟阻尼系数，包含有功控制模块APCM和无功控制模块QPCM两个部分；Step 1.1: Construct the VSG equivalent output power model, which includes the parameters virtual governor VG, virtual inertia, and virtual damping coefficient, including two parts: active power control module APCM and reactive power control module QPCM;

步骤1.1.1：有功控制模块APCM由VG和虚拟机械转动模块两部分组成，分别模拟SG的调速器和转子的机械运动方程，具体如下：Step 1.1.1: The active power control module APCM is composed of VG and virtual mechanical rotation module, which respectively simulate the mechanical motion equations of the governor and rotor of SG, as follows:

Figure BDA0002146672940000091
Figure BDA0002146672940000091

其中，Pei、Prefi分别为微电网中第i台VSG(VSGi,i＝1,2,3)的输出有功功率和控制器设置的有功功率参考值；

Figure BDA0002146672940000092
分别为VSGi的虚拟转动惯量和虚拟阻尼系数，用于模拟SG的转子运动特性；ωn、ωi分别为VSGi的额定角速度和VSGi的虚拟转子角速度,ωni＝ωn-ωi代表两者之差；δni表示VSGi虚拟转子的相对位移角，同时也是QPCM中输出电压与额定电压的相角差；
Figure BDA0002146672940000093
和
Figure BDA0002146672940000094
表示VSGi中VG输出的虚拟机械功率和虚拟下垂系数。本实施例中三台VSG的额定容量相同，有功功率参考值Prefi均为6kW，额定角速度ωn＝314rad/s；Among them, P ei and P refi are respectively the output active power of the i-th VSG (VSGi,i=1,2,3) in the microgrid and the active power reference value set by the controller;
Figure BDA0002146672940000092
are the virtual moment of inertia and virtual damping coefficient of VSGi, which are used to simulate the rotor motion characteristics of SG; The difference; δ ni represents the relative displacement angle of the VSGi virtual rotor, and is also the phase angle difference between the output voltage and the rated voltage in QPCM;
Figure BDA0002146672940000093
and
Figure BDA0002146672940000094
Indicates the virtual mechanical power and virtual droop coefficient of VG output in VSGi. In this embodiment, the rated capacity of the three VSGs is the same, the active power reference value P refi is 6kW, and the rated angular velocity ω n =314rad/s;

步骤1.1.2：无功控制模块QPCM，在于模拟VSG的无功-电压调节特性，具体如下：Step 1.1.2: The reactive power control module QPCM is to simulate the reactive power-voltage regulation characteristics of VSG, as follows:

Figure BDA0002146672940000095
Figure BDA0002146672940000095

其中，Qei，Qrefi分别为VSGi的输出无功功率和控制器设置的无功功率参考值；Ei、En分别代表VSGi输出的电压幅值和额定电压幅值；

Figure BDA0002146672940000096
为QPCM下垂系数。本实施例中三台VSG的无功功率参考值Qrefi均为1kVA，微电网的额定电压幅值En＝380V；Among them, Q ei and Q refi are the output reactive power of VSGi and the reference value of reactive power set by the controller; E i and En represent the voltage amplitude and rated voltage amplitude of VSGi output respectively;
Figure BDA0002146672940000096
is the QPCM droop coefficient. In this embodiment, the reactive power reference values Q refi of the three VSGs are all 1kVA, and the rated voltage amplitude of the microgrid E n =380V;

步骤1.2：构建联络线路等效传输功率模型：Step 1.2: Construct the equivalent transmission power model of the tie line:

Figure BDA0002146672940000097
Figure BDA0002146672940000097

其中，

Figure BDA0002146672940000098
分别代表微电网中VSGi与电网连接的等效有功和无功传输功率；
Figure BDA0002146672940000099
分别代表传输线路阻抗和感抗；本实施例中传输线路阻抗和感抗
Figure BDA00021466729400000910
分别为0.64Ω/km和0.10Ω/km，微电网的额定电压的幅值En＝380V，相角δn＝0°；in,
Figure BDA0002146672940000098
represent the equivalent active and reactive transmission power of VSGi connected to the grid in the microgrid, respectively;
Figure BDA0002146672940000099
Represent transmission line impedance and inductive reactance respectively; Transmission line impedance and inductive reactance in this embodiment
Figure BDA00021466729400000910
0.64Ω/km and 0.10Ω/km respectively, the amplitude of the rated voltage of the microgrid E n =380V, and the phase angle δ n =0°;

步骤1.3：考虑系统负载情况，建立并网微电网的功率平衡方程：Step 1.3: Considering the system load, establish the power balance equation of the grid-connected microgrid:

Figure BDA0002146672940000101
Figure BDA0002146672940000101

其中，PLi、QLi分别代表微电网所连接负载的有功功率和无功功率；本实施例中微电网所连接负载的有功功率PLi无功功率QLi分别为20kW和4kVA；Wherein, P Li and Q Li respectively represent the active power and reactive power of the load connected to the microgrid; the active power P Li and the reactive power Q Li of the load connected to the microgrid in this embodiment are 20kW and 4kVA respectively;

步骤2：利用首次积分法构建考虑VG、虚拟惯量、虚拟阻尼系数的多台VSG并联运行的并网微电网的李雅普诺夫能量函数，计算微电网系统中的总能量VTOT；Step 2: Use the first integral method to construct the Lyapunov energy function of the grid-connected microgrid with multiple VSGs running in parallel considering VG, virtual inertia, and virtual damping coefficient, and calculate the total energy V TOT in the microgrid system;

步骤2.1：构建考虑权重关系的动能总能量函数VKE：Step 2.1: Construct the kinetic energy total energy function V KE considering the weight relationship:

步骤2.1.1：设置各动能项的权重因子

Figure BDA0002146672940000102
其中Mki为动能能量函数的阈值，i＝1,2,3；Step 2.1.1: Set the weight factor of each kinetic energy item
Figure BDA0002146672940000102
Where M ki is the threshold value of the kinetic energy function, i=1,2,3;

步骤2.1.2：构建微电网中所有VSG的虚拟惯量模拟的虚拟转子加/减速所引起的动能，具体如下：Step 2.1.2: Construct the kinetic energy caused by the virtual rotor acceleration/deceleration simulated by the virtual inertia of all VSGs in the microgrid, as follows:

Figure BDA0002146672940000103
Figure BDA0002146672940000103

其中，Mk1＝140；Among them, M k1 =140;

步骤2.1.3：构建虚拟阻尼系数和虚拟调速器的下垂系数所消耗的系统动能函数，具体如下：Step 2.1.3: Construct the system kinetic energy function consumed by the virtual damping coefficient and the droop coefficient of the virtual governor, as follows:

Figure BDA0002146672940000104
Figure BDA0002146672940000104

其中，ts＝6s，Mk2＝170，

Figure BDA0002146672940000105
表示故障后系统的稳定平衡点处的转动角频率；Among them, t s =6s, M k2 =170,
Figure BDA0002146672940000105
Indicates the rotational angular frequency at the stable equilibrium point of the system after the fault;

步骤2.1.4：构建进行频率和功率的一次调节时所消耗的动能，具体如下：Step 2.1.4: Construct the kinetic energy consumed by one adjustment of frequency and power, as follows:

Figure BDA0002146672940000106
Figure BDA0002146672940000106

其中，χ＝dω/dt，Mk3＝500；Wherein, χ=dω/dt, M k3 =500;

步骤2.1.5：根据步骤2.1.1-2.14构建动能总能量函数VKE：Step 2.1.5: Construct the total kinetic energy function V KE according to steps 2.1.1-2.14:

VKE＝(VKE1+VKE2+VKE3) (8)V KE ＝(V KE1 +V KE2 +V KE3 ) (8)

步骤2.2：构建考虑权重关系的势能能量函数VPE：Step 2.2: Construct the potential energy function V PE considering the weight relationship:

步骤2.2.1：设置不同势能项的权重因子

Figure BDA0002146672940000111
其中Mpi为势能能量函数的阈值，i＝1,2,3,4；Step 2.2.1: Set weight factors for different potential energy items
Figure BDA0002146672940000111
Where M pi is the threshold value of the potential energy function, i=1,2,3,4;

步骤2.2.2：构建微电网系统中所有VSG的有功参考功率和有功负载引起的势能能量函数，具体如下：Step 2.2.2: Construct the active reference power of all VSGs in the microgrid system and the potential energy function caused by the active load, as follows:

Figure BDA0002146672940000112
Figure BDA0002146672940000112

其中，MP1＝1.8×103；Among them, M P1 =1.8×10 3 ;

步骤2.2.3：构建VSG的无功参考功率和无功负载引起的势能能量函数，具体如下：Step 2.2.3: Construct the reactive reference power of the VSG and the potential energy function caused by the reactive load, as follows:

Figure BDA0002146672940000113
Figure BDA0002146672940000113

其中，

Figure BDA0002146672940000114
为故障后系统电压的幅值，MP2＝5×103；in,
Figure BDA0002146672940000114
is the magnitude of the system voltage after the fault, M P2 =5×10 3 ;

步骤2.2.4：构建VSG与电网之间联络线路上传输的有功功率所代表的势能能量函数，具体如下：Step 2.2.4: Construct the potential energy function represented by the active power transmitted on the connection line between the VSG and the grid, as follows:

Figure BDA0002146672940000115
Figure BDA0002146672940000115

其中，

Figure BDA0002146672940000116
Figure BDA0002146672940000117
为故障后系统电压的相角，MP3＝1.12×103；in,
Figure BDA0002146672940000116
Figure BDA0002146672940000117
is the phase angle of the system voltage after the fault, M P3 =1.12×10 3 ;

步骤2.2.5：构建VSG与电网之间联络线路上传输的无功功率所代表的势能能量函数，具体如下：Step 2.2.5: Construct the potential energy function represented by the reactive power transmitted on the connection line between the VSG and the grid, as follows:

Figure BDA0002146672940000118
Figure BDA0002146672940000118

其中，MP4＝7.33×103；Among them, M P4 =7.33×10 3 ;

步骤2.2.6：根据步骤2.2.1-2.2.5,构建势能总能量函数，具体如下：Step 2.2.6: According to steps 2.2.1-2.2.5, construct the potential energy total energy function, as follows:

VPE＝VPE1+VPE2+VPE3+VPE4 (13)V PE ＝V PE1 +V PE2 +V PE3 +V PE4 (13)

步骤2.3：计算并网微电网的总能量函数VTOT：Step 2.3: Calculate the total energy function V TOT of the grid-connected microgrid:

VTOT＝VPE+VKE。 (14)V TOT =V PE +V KE . (14)

本实施例中，设计多台VSG并联运行的微电网稳定运行到6s时，在并网处发生短路故障，6.1s时故障切除。微电网稳定运行时，微电网的总能量为1kJ，发生故障后，总能量的变化如图4所示。In this embodiment, when a microgrid with multiple VSGs in parallel is designed to run stably for 6s, a short-circuit fault occurs at the grid-connected point, and the fault is removed at 6.1s. When the microgrid is running stably, the total energy of the microgrid is 1kJ. After a fault occurs, the change of the total energy is shown in Figure 4.

步骤3：根据现场需求设置能量函数的阈值，判断系统的运行状态；Step 3: Set the threshold of the energy function according to the site requirements, and judge the operating status of the system;

Figure BDA0002146672940000121
Figure BDA0002146672940000121

其中，MAVE为系统稳定运行时能量函数的阈值，VTOT为微电网系统中的总能量。Among them, M AVE is the threshold value of the energy function when the system is running stably, and V TOT is the total energy in the microgrid system.

本实施例中为了使系统对故障的反应更灵敏，设置总能量函数的阈值MAVE＝VTOT＝1kJ，在图4中5.8s至6s这段时间，计算到的系统总能量小于等于1kJ，判断系统处于稳定状态；In this embodiment, in order to make the system respond more sensitively to faults, the threshold of the total energy function M AVE =V TOT =1kJ is set. During the period from 5.8s to 6s in Figure 4, the calculated total system energy is less than or equal to 1kJ. Judging that the system is in a stable state;

步骤4:若系统稳定运行，执行步骤2继续计算；Step 4: If the system runs stably, perform step 2 to continue the calculation;

当6s时计算到系统总能量VTOT＞1kJ时，根据上述方法可判断系统出现故障。When the total system energy V TOT >1kJ is calculated at 6s, it can be judged that the system is faulty according to the above method.

步骤5：若系统发生故障，则采用主导不稳定平衡点法，计算系统的临界能量Vcr；Step 5: If the system fails, use the dominant unstable equilibrium point method to calculate the critical energy V cr of the system;

步骤5.1：计算系统故障轨线至故障清除时刻以及出口点，具体如下：Step 5.1: Calculate the system fault trajectory to the fault clearing time and exit point, as follows:

Figure BDA0002146672940000122
Figure BDA0002146672940000122

步骤5.2：以出口点为初值，采用Gear方法计算故障后梯度系统的最小梯度点，具体如下：Step 5.2: Take the exit point as the initial value, and use the Gear method to calculate the minimum gradient point of the gradient system after the failure, as follows:

Figure BDA0002146672940000123
Figure BDA0002146672940000123

其中，

Figure BDA0002146672940000124
为最小梯度点；in,
Figure BDA0002146672940000124
is the minimum gradient point;

步骤5.3：以最小梯度点

Figure BDA0002146672940000125
为初值，求解系统的功率平衡方程得到系统的稳定平衡点和主导不稳定平衡点，具体如下：Step 5.3: Take the minimum gradient point
Figure BDA0002146672940000125
As the initial value, solve the power balance equation of the system to obtain the stable equilibrium point and dominant unstable equilibrium point of the system, as follows:

Figure BDA0002146672940000131
Figure BDA0002146672940000131

步骤5.4：根据系统主导不稳定平衡点处的状态量，计算出微电网并网系统的临界能量Vcr：Step 5.4: Calculate the critical energy V cr of the microgrid grid-connected system according to the state quantity at the dominant unstable equilibrium point of the system:

Figure BDA0002146672940000132
Figure BDA0002146672940000132

其中，

Figure BDA0002146672940000133
分别为系统故障后微电网中VSGi的稳定平衡点和不稳定平衡点；
Figure BDA0002146672940000134
分别为微电网稳定运行时VSGi的虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数；
Figure BDA0002146672940000135
分别表示故障后系统的稳定平衡点处的转动角频率，电压的相角和幅值，χ＝dω/dt，ts为故障发生时间。in,
Figure BDA0002146672940000133
are the stable equilibrium point and unstable equilibrium point of VSGi in the microgrid after system failure, respectively;
Figure BDA0002146672940000134
are the virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient of VSGi when the microgrid is in stable operation;
Figure BDA0002146672940000135
respectively represent the rotational angular frequency at the stable equilibrium point of the system after the fault, the phase angle and amplitude of the voltage, χ=dω/dt, and t s is the fault occurrence time.

本实施例中当故障发生时间ts＝6s时，计算得到系统临界能量Vcr＝3.25kJ。In this embodiment, when the fault occurrence time t s =6s, the system critical energy V cr =3.25kJ is calculated.

步骤6：启动基于能量函数的VSG虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数自适应控制方法；Step 6: Start the adaptive control method of VSG virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient based on energy function;

步骤6.1：基于能量函数的VSG虚拟惯量自适应控制方法：Step 6.1: VSG virtual inertia adaptive control method based on energy function:

Figure BDA0002146672940000136
Figure BDA0002146672940000136

其中，微电网稳定运行时VSGi的虚拟惯量最大值

Figure BDA0002146672940000137
能量函数的阈值MAVE＝1kJ；Among them, the maximum value of the virtual inertia of VSGi when the microgrid is running stably
Figure BDA0002146672940000137
The threshold MAVE of the energy function = 1kJ;

步骤6.2：基于能量函数的VSG虚拟阻尼系数的自适应控制方法：Step 6.2: Adaptive control method of VSG virtual damping coefficient based on energy function:

Figure BDA0002146672940000141
Figure BDA0002146672940000141

其中，微电网稳定运行时VSGi的虚拟阻尼系数最大值

Figure BDA0002146672940000142
Among them, the maximum value of the virtual damping coefficient of VSGi when the microgrid is running stably
Figure BDA0002146672940000142

步骤6.3：基于能量函数设计VG下垂系数的自适应控制方法：Step 6.3: Design an adaptive control method for the VG droop coefficient based on the energy function:

Figure BDA0002146672940000143
Figure BDA0002146672940000143

其中，微电网稳定运行时VSGi的VG下垂系数最小值

Figure BDA0002146672940000144
Among them, the minimum value of the VG droop coefficient of VSGi when the microgrid is running stably
Figure BDA0002146672940000144

步骤6.4：基于能量函数设计QPCM下垂系数的自适应控制方法：Step 6.4: Design the adaptive control method of QPCM droop coefficient based on the energy function:

Figure BDA0002146672940000145
Figure BDA0002146672940000145

其中，微电网稳定运行时VSGi的QPCM下垂系数最大值

Figure BDA0002146672940000146
Among them, the maximum value of the QPCM droop coefficient of VSGi when the microgrid is running stably
Figure BDA0002146672940000146

本实施例中VSG的虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数根据能量函数的自适应控制变化如图5所示，其具体取值如图6所示。In this embodiment, the changes of the virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient according to the energy function of the adaptive control of the VSG are shown in FIG. 5 , and their specific values are shown in FIG. 6 .

步骤7：在6.1s时故障清除；Step 7: The fault is cleared at 6.1s;

步骤8：执行步骤2计算故障清除时刻，微电网系统中的总能量Vcl；Step 8: Perform step 2 to calculate the total energy V cl in the microgrid system at the moment of fault clearing;

步骤9：将故障清除时刻微电网系统中的总能量Vcl与临界能量Vcr作比较，分析判断微电网的稳定性。Step 9: Compare the total energy V cl in the microgrid system at the moment of fault clearing with the critical energy V cr to analyze and judge the stability of the microgrid.

Figure BDA0002146672940000147
Figure BDA0002146672940000147

本实施例中，因应用了自适应控制方法，故障清除后微电网系统中的总能量Vcl低于临界能量Vcr，根据上述方法可判断系统稳定。In this embodiment, due to the application of the adaptive control method, the total energy V cl in the microgrid system is lower than the critical energy V cr after the fault is cleared, and the system can be judged to be stable according to the above method.

如图4所示，若没有虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数的自适应控制，则系统的能量在6.08s左右将越过系统临界能量Vcr，根据上述方法可判断系统失稳，此时若不及时切除故障，必定给微电网系统带来巨大的损害，当6.1s故障切除之后，系统总能量在6.12s时降到临界能量Vcr之下，可判断系统恢复稳定。而加入了虚拟惯量、虚拟阻尼系数、VG下垂系数和QPCM下垂系数的自适应控制之后，系统在故障期间的总能量相对较小，而且增长趋势与不加入自适应控制的增长趋势比较更加缓慢，为故障切除争取了有效的时间，在6.1s故障切除时，系统总能量VTOT没有超出临界能量Vcr的值，系统没有出现失稳状态，保持了良好的暂态稳定性。As shown in Fig. 4, if there is no adaptive control of virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient, the energy of the system will exceed the system critical energy V cr at about 6.08s. According to the above method, the system failure can be judged At this time, if the fault is not removed in time, it will definitely bring huge damage to the microgrid system. When the 6.1s fault is removed, the total energy of the system drops below the critical energy V cr at 6.12s, and the system can be judged to be stable. After adding the adaptive control of virtual inertia, virtual damping coefficient, VG droop coefficient and QPCM droop coefficient, the total energy of the system during the fault period is relatively small, and the growth trend is slower than that without adaptive control. The effective time was gained for the fault removal. When the fault was removed at 6.1s, the total system energy V TOT did not exceed the value of the critical energy V cr , and the system did not appear in an unstable state, maintaining good transient stability.

Claims (9)

1. A micro-grid transient stability control method containing multiple virtual synchronous machines is characterized by comprising the following steps:
step 1: constructing a power balance model of a grid-connected microgrid with a plurality of VSGs running in parallel, wherein the model comprises a VSG equivalent output power model, a connection line equivalent transmission power model and a power balance equation of the grid-connected microgrid;
step 2: utilizing a first integration method to construct a Lyapunov energy function V of a grid-connected microgrid with VG, virtual inertia and virtual damping coefficients considered and multiple VSGs running in parallel TOT Calculating the total energy in the microgrid system;
and step 3: setting a threshold value of an energy function according to the field requirement, and judging the running state of the system;
step 4, if the system runs stably, executing the step 2 to continue calculating;
and 5: if the system fails, calculating the critical energy V of the system by adopting a dominant unstable balance point method cr ；
Step 6: starting a VSG virtual inertia, a virtual damping coefficient, a VG droop coefficient and a QPCM droop coefficient self-adaptive control method based on an energy function;
and 7: judging whether the fault is cleared;
and step 8: step 2 is executed to calculate the total energy V in the microgrid system at the moment of fault clearance cl ；
And step 9: total energy V in microgrid system at fault clearing time cl And critical energy V cr And comparing, analyzing and judging the stability of the microgrid.
2. The method according to claim 1, wherein the method comprises the steps of: the VSG equivalent output power model in the step 1 comprises a parameter virtual speed regulator VG, a virtual inertia and a virtual damping coefficient and comprises an active control module APCM and a reactive control module QPCM;
the active control module APCM consists of two parts, namely a VG and a virtual mechanical rotation module, and respectively simulates a SG speed regulator and a mechanical motion equation of a rotor, wherein the active control module APCM specifically comprises the following components:
Figure FDA0002146672930000011
wherein, P ei 、P refi An active power reference value set for the output active power of the ith VSG (VSGi, i =1,2.., N) in the microgrid and the controller respectively;
Figure FDA0002146672930000012
the virtual moment of inertia and the virtual damping coefficient are respectively VSGi and are used for simulating the rotor motion characteristic of SG; omega n 、ω i Rated angular velocity of VSGi and virtual rotor angular velocity of VSGi, ω ni ＝ω n -ω i Represents the difference between the two; delta. For the preparation of a coating ni The relative displacement angle of the VSGi virtual rotor is represented, and the phase angle difference between the output voltage and the rated voltage in the QPCM is also represented;
Figure FDA0002146672930000013
and
Figure FDA0002146672930000014
representing the virtual mechanical power and the virtual droop coefficient of the VG output in the VSGi;
the reactive power control module QPCM simulates the reactive-voltage regulation characteristics of the VSG, as follows:
Figure FDA0002146672930000021
wherein Q is ei ，Q refi The reactive power reference value is respectively set for the output reactive power of the VSGi and the controller; e i 、E n Respectively representing the voltage amplitude and the rated voltage amplitude of the VSGi output;
Figure FDA0002146672930000022
the QPCM droop coefficient.
3. The method according to claim 1, wherein the method comprises the steps of: in the step 1, an equivalent transmission power model of the contact line is constructed, and a calculation formula is as follows:
Figure FDA0002146672930000023
wherein,
Figure FDA0002146672930000024
respectively representing equivalent active and reactive transmission power of VSGi in the micro-grid connected with the grid;
Figure FDA0002146672930000025
representing the transmission line impedance and the inductive reactance, respectively; delta ni Representing the phase angle difference between the rated voltage of the power grid and the output voltage of the VSG; e i 、E n Representing the voltage magnitude of the VSGi output and the nominal voltage magnitude, respectively.
4. The method according to claim 1, wherein the method comprises: in the step 1, the power balance equation of the grid-connected microgrid considers the system load condition, and the following equation is constructed:
Figure FDA0002146672930000026
wherein, P refi 、Q refi The active power reference value and the reactive power reference value are respectively set for the controller; omega n 、ω i A nominal angular velocity of VSGi and a virtual rotor angular velocity of VSGi, respectively; e i 、E n Respectively representing the voltage amplitude and the rated voltage amplitude output by VSGi;
Figure FDA0002146672930000027
respectively representing the impedance and the inductive reactance of the communication line;
Figure FDA0002146672930000028
virtual moment of inertia and virtual damping coefficient of VSGi respectively; delta. For the preparation of a coating ni Representing the phase angle difference between the rated voltage of the power grid and the VSGi output voltage; p Li 、Q Li Respectively representing the active power and the reactive power of a load connected with the microgrid;
Figure FDA0002146672930000029
a virtual droop coefficient representing the VG output in VSGi;
Figure FDA00021466729300000210
the QPCM droop coefficient.
5. The method according to claim 1, wherein the method comprises: in the step 2, a first integration method is utilized to construct a Lyapunov energy function V of a grid-connected microgrid with a plurality of VSGs running in parallel and considering VG, virtual inertia and virtual damping coefficient TOT The process of (2) is as follows:
step 2.1: constructing a kinetic energy function V taking into account a weight relationship KE ；
Step 2.1.1: setting weight factors for kinetic energy items
Figure FDA0002146672930000031
Wherein M is ki Threshold for kinetic energy function, i =1,2,3;
step 2.1.2: the method comprises the following steps of constructing kinetic energy caused by acceleration/deceleration of virtual rotors simulated by virtual inertia of all VSGs in the microgrid, and specifically comprising the following steps:
Figure FDA0002146672930000032
wherein,
Figure FDA0002146672930000033
virtual moment of inertia, ω, for VSGi n Rated angular velocity, ω, of VSGi ni Is the difference between the rated angular velocity of VSGi and the virtual rotor angular velocity of VSGi;
step 2.1.3: the method comprises the following steps of constructing a system kinetic energy function consumed by a virtual damping coefficient and a droop coefficient of a virtual speed regulator, wherein the system kinetic energy function comprises the following specific steps:
Figure FDA0002146672930000034
wherein, t s In order to be the time when the failure occurs,
Figure FDA0002146672930000035
indicating the rotational angular frequency at the stable equilibrium point of the system after a fault,
Figure FDA0002146672930000036
for the virtual damping coefficient of VSGi,
Figure FDA0002146672930000037
a virtual droop coefficient representing the VG output in VSGi;
step 2.1.4: the kinetic energy consumed in performing one adjustment of frequency and power is constructed as follows:
Figure FDA0002146672930000038
wherein χ = d ω/dt;
step 2.1.5: constructing a kinetic energy total energy function V according to the steps 2.1.1-2.14 KE ：
V KE ＝(V KE1 +V KE2 +V KE3 ) (8)
Step 2.2: constructing a potential energy function V considering the weight relation PE ；
Step 2.2.1: setting weight factors of different potential energy items
Figure FDA0002146672930000039
Wherein M is pi Threshold for potential energy function, i =1,2,3,4;
step 2.2.2: the method comprises the following steps of constructing potential energy functions caused by active reference power and active loads of all VSGs in the micro-grid system, and specifically comprising the following steps:
Figure FDA0002146672930000041
wherein, delta ni Representing the phase angle difference, P, between the rated voltage of the grid and the VSGi output voltage refi Active power reference value, P, set for the controller Li Active power for a load connected to the microgrid;
step 2.2.3: constructing a potential energy function caused by reactive reference power and reactive load of the VSG, which comprises the following steps:
Figure FDA0002146672930000042
wherein,
Figure FDA0002146672930000043
amplitude of the system voltage after a fault, Q refi Reactive power reference value, Q, set for the controller Li Reactive power of loads connected to the microgrid, E ni The difference value of the rated voltage of the power grid and the rated voltage of the ith VSG in the micro-grid is obtained;
step 2.2.4: constructing a potential energy function represented by active power transmitted on a connecting line between the VSG and a power grid, wherein the potential energy function is as follows:
Figure FDA0002146672930000044
wherein,
Figure FDA0002146672930000045
Figure FDA0002146672930000046
is the phase angle of the system voltage after the fault,
Figure FDA0002146672930000047
respectively representing the impedance and inductive reactance of the interconnection line, E i The voltage amplitude output for VSGi;
step 2.2.5: constructing a potential energy function represented by reactive power transmitted on a connecting line between the VSG and the power grid, wherein the potential energy function is as follows:
Figure FDA0002146672930000048
wherein,
Figure FDA0002146672930000049
for QPCM sag factor, E n A rated voltage amplitude of VSGi;
step 2.2.6: according to the steps 2.2.1-2.2.5, a potential energy and total energy function is constructed, which is as follows:
V PE ＝V PE1 +V PE2 +V PE3 +V PE4 (13)
step 2.3: calculating total energy function V of grid-connected microgrid TOT ：
V TOT ＝V PE +V KE 。 (14)
6. The method according to claim 1, wherein the method for determining the operating state of the system in step 3 is as follows:
Figure FDA0002146672930000051
wherein M is AVE Threshold value of energy function, V, for stable operation of system TOT The total energy in the microgrid system calculated for step 2 in claim 1.
7. The method according to claim 1, wherein the critical energy V of the system is calculated by using a dominant unstable equilibrium point method in the step 5 cr The process of (2) is as follows:
step 5.1: calculating the time from the system fault track to the fault clearing time and the exit point, specifically as follows:
Figure FDA0002146672930000052
wherein,
Figure FDA0002146672930000053
virtual moment of inertia and virtual damping coefficient, P, of VSGi, respectively refi Active power reference value, omega, set for the controller n 、ω i Rated angular velocity of VSGi and virtual rotor angular velocity of VSGi, ω ni ＝ω n -ω i Represents the difference between the two, P ei For the output active power, delta, of the ith VSG in the microgrid i Is the phase angle of the rated voltage of the ith station VSG in the microgrid,
Figure FDA0002146672930000054
a virtual droop coefficient representing the VG output in VSGi;
and step 5.2: taking the exit point as an initial value, and calculating the minimum gradient point of the gradient system after the fault by adopting a Gear method, wherein the method specifically comprises the following steps:
Figure FDA0002146672930000055
wherein,
Figure FDA0002146672930000056
is the minimum gradient point;
step 5.3: at the point of minimum gradient
Figure FDA0002146672930000057
As an initial value, solving a power balance equation of the system to obtain a stable balance point and a dominant unstable balance point of the system, which are specifically as follows:
Figure FDA0002146672930000061
wherein, delta ni Representing the phase angle difference between the rated voltage of the grid and the VSGi output voltage,
Figure FDA0002146672930000062
respectively representing the impedance and inductive reactance, P, of the interconnection line Li Active power of loads connected to the microgrid, E i 、E n Respectively representing the voltage amplitude and the rated voltage amplitude of the VSGi output;
step 5.4: calculating critical energy V of the microgrid system according to state quantity at dominant unstable balance point of the system cr ：
Figure FDA0002146672930000063
Wherein,
Figure FDA0002146672930000064
respectively setting a stable balance point and an unstable balance point of VSGi in the microgrid after the system fault;
Figure FDA0002146672930000065
respectively representing the virtual inertia, the virtual damping coefficient, the VG droop coefficient and the QPCM droop coefficient of VSGi during the stable operation of the microgrid;
Figure FDA0002146672930000066
representing the angular frequency of rotation, the phase angle and the amplitude of the voltage, χ = d ω/dt, t, respectively, at the point of stable equilibrium of the system after a fault s Is the time of occurrence of the fault.
8. The method according to claim 1, wherein the adaptive control method for the transient stability of the microgrid with multiple virtual synchronous machines is based on the energy function in the step 6, and comprises the following steps:
step 6.1: the VSG virtual inertia self-adaptive control method based on the energy function comprises the following steps:
Figure FDA0002146672930000071
wherein,
Figure FDA0002146672930000072
respectively the virtual inertia and the maximum value of the virtual inertia, M, of VSGi when the micro-grid operates stably AVE A threshold value that is a function of total energy;
step 6.2: the self-adaptive control method of the VSG virtual damping coefficient based on the energy function comprises the following steps:
Figure FDA0002146672930000073
wherein,
Figure FDA0002146672930000074
respectively representing the virtual damping coefficient and the maximum value of the virtual damping coefficient of VSGi when the micro-grid is in stable operation;
step 6.3: designing an adaptive control method of a VG droop coefficient based on an energy function:
Figure FDA0002146672930000075
wherein,
Figure FDA0002146672930000076
respectively representing the VG droop coefficient and the VG droop coefficient minimum value of VSGi during the stable operation of the microgrid;
step 6.4: the self-adaptive control method for designing the QPCM droop coefficient based on the energy function is as follows:
Figure FDA0002146672930000077
in the formula,
Figure FDA0002146672930000078
and respectively representing the maximum value of the QPCM droop coefficient and the QPCM droop coefficient of the VSGi during the stable operation of the micro-grid.
9. The method according to claim 1, wherein the step 9 is to remove the total energy V in the microgrid at the fault clearing time cl And critical energy V cr Comparing, analyzing and judging the stability of the microgrid as follows:
Figure FDA0002146672930000081
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