Optimal Power Flow Using Firefly Algorithm with Unified Power Flow Controller

Firefly algorithm is the new intelligent algorithm used for all complex engineering optimization problems. Power system has many complex optimization problems one of which is the optimal power flow (OPF). Basically, it is minimizing optimization problem and subjected to many complex objective functions and constraints. Hence, firefly algorithm is used to solve OPF in this paper. The aim of the firefly is to optimize the control variables, namely generated real power, voltage magnitude and tap setting of transformers. Flexible AC Transmission system (FACTS) devices may used in the power system to improve the quality of the power supply and to reduce the cost of the generation. FACTS devices are classified into series, shunt, shunt-series and series-series connected devices. Unified power flow controller (UPFC) is shunt-series type device that posses all capabilities to control real, reactive powers, voltage and reactance of the connected line in the power system. Hence, UPFC is included in the considered IEEE 30 bus for the OPF solution.

Investigation of Real Power Flow Control of AI Based MC-UPFC in FACTS Controllers

The power consumption is rapidly increased due to ASD(Adjustable Speed Drives)and automation in industries and large consumption of electricity in domestic regions increased the concern of the power quality.The quality of the power received in the distribution system is altered because of the losses in the transmission system.The losses in the transmission system are mitigated using the FACTS(Flexible AC Transmission System)controller,among these controllers UPFC(Unified Power Flow Controller)plays a vital role in controlling the shunt and series reactive powers in the bus of the power system.The conventional topology of the UPFC consists of AC-DC converter and energy stored in the DC link and DC-AC converter injected a voltage in series to the bus which is to be controlled.Whereas a new topology based on matrix converter can replace the dual converters and perform the required task.The construction of 2-bus,7-bus and IEEE-14-bus power system is designed and modeled.MC-UPFC(Matrix Converter Based Unified Power Flow Controller)is designed and constructed.The MC-UPFC is the rich topology in the FACTS which is capable of controlling both the transmission parameters simultaneously with the switching technique of direct power control by the smooth sliding control which gives less ripple in the injecting control parameters such as control voltage(Vc)and voltage angle(α).By implementing MC-UPFC the real and reactive power can be controlled simultaneously and independently.The control techniques were designed based on the PID(Proportional Integral Derivative)with sliding surface power control,FLC(Fuzzy Logic Controller)and ANN(Artificial Neural Network)and the performances of Vc andαof the controllers are investigated.Hence the sliding surface and relevant control switching state of the MC can be controlled by the FLC which gives the robust and autonomous decision made in the selection of the appropriate switching state for the effective real power control in the power system.The work has been carried out in the MATLAB Simulink simulator which gives the finest controlling features and simple design procedures and monitoring of the output.

Harmonic influence analysis of unified power flow controller based on modular multilevel converter

The unified power flow controller(UPFC)based on modular multilevel converter(MMC) is the most creative flexible ac transmission system(FACTS) device. In theory, the output voltage of the series MMC in MMCUPFC can be regulated from 0 to the rated value. However,there would be relatively large harmonics in the output voltage if the voltage modulation ratio is small. In order to analyze the influence of MMC-UPFC on the harmonics of the power grid, the theoretical calculation method and spectra of the output voltage harmonics of MMC are presented. Subsequently, the calculation formulas of the harmonics in the power grid with UPFC are proposed. Based on it, the influence of UPFC on the grid voltage harmonics is evaluated, when MMC-UPFC is operated with different submodular numbers and voltage modular ratios. Eventually, the proposed analysis method is validated using digital simulation. The study results would provide guideline for the design and operation of MMC-UPFC project.

A multi-objective gravitational search algorithm based approach of power system stability enhancement with UPFC

On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UPFC supplementary controller to enhance the dynamic stability of a power system is evaluated by measuring the electromechanical controllability through singular value decomposition （SVD） analysis. This controller is tuned to simultaneously shift the undamped electromeehanical modes to a prescribed zone in the s-plane. The problem of robust UPFC based damping controller is formulated as an optimization problem according to the eigenvalue-based multi-objective function comprising the damping factor, and the damping ratio of the undamped electromechanical modes to be solved using gravitational search algorithm （GSA） that has a strong ability to find the most optimistic results. The different loading conditions are simulated on a SMIB system and the rotor speed deviation, internal voltage deviation, DC voltage deviation and electrical power deviation responses are studied with the effect of this flexible AC transmission systems （FACTS） controller. The results reveal that the tuned GSA based UPFC controller using the proposed multi-objective function has an excellent capability in damping power system with low frequency oscillations and greatly enhances the dynamic stability of the power systems.

Mitigation of power system forced oscillations based on unified power flow controller

Forced oscillations(FOs), or low-frequency oscillations(LFOs) caused by periodic, continuous, small power disturbances, threaten the security and stability of power systems.Flexible AC transmission system(FACTS)devices can effectively mitigate LFOs via stability control.We propose a novel method that mitigates FOs by shifting the resonant frequency.Based on the features of the linearized swing equation of a generator, a resonant frequency shift can be achieved by controlling the synchronous torque coefficient using a unified power flow controller(UPFC).Because of the resonance mechanism, the steady-state response of an FO can be effectively mitigated when the resonant frequency changes from the original one, which was close to the disturbance frequency.The principle is that a change in resonant frequency affects the resonance condition.Simulations are conducted in a single-machine infinite-bus(SMIB) system, and the simulation results verify that the method is straightforward to implement and can significantly mitigate FOs.The controller robustness when the resonant frequency is not accurately estimated is also analyzed in the simulations.

Subsynchronous resonance and its mitigation for power system with unified power flow controller

Control strategy of unified power flow controller(UPFC)utilizing dq decoupling control is deduced in this paper,which can closely follow the control orders of the active and reactive power.The subsynchronous resonance(SSR)characteristics of a series compensated system equipped with UPFC are studied,and the results reveal that SSR characteristics of the system may vary significantly with UPFC in service or not.Consequently,supplementary subsynchronous damping controller(SSDC)for UPFC is proposed and investigated,and the effectiveness of the proposed SSDC is verified by damping torque analysis and time domain simulations.

A Data Driven Security Correction Method for Power Systems with UPFC

The access of unified power flow controllers(UPFC)has changed the structure and operation mode of power grids all across the world,and it has brought severe challenges to the traditional real-time calculation of security correction based on traditionalmodels.Considering the limitation of computational efficiency regarding complex,physical models,a data-driven power system security correction method with UPFC is,in this paper,proposed.Based on the complex mapping relationship between the operation state data and the security correction strategy,a two-stage deep neural network(DNN)learning framework is proposed,which divides the offline training task of security correction into two stages:in the first stage,the stacked auto-encoder(SAE)classification model is established,and the node correction state(0/1)output based on the fault information;in the second stage,the DNN learningmodel is established,and the correction amount of each action node is obtained based on the action nodes output in the previous stage.In this paper,the UPFC demonstration project of NanjingWest Ring Network is taken as a case study to validate the proposed method.The results show that the proposed method can fully meet the real-time security correction time requirements of power grids,and avoid the inherent defects of the traditional model method without an iterative solution and can also provide reasonable security correction strategies for N-1 and N-2 faults.

UPFC Based Real-Time Optimization of Power Systems for Dynamic Voltage Regulation

Flexible alternating current transmission system(FACTS)components are used to utilize the electrical transmission lines at their optimum capacity.The best way to achieve this optimization is to manage the active and reactive power flows.A unified power flow controller(UPFC)is one of the most significant devices developed for the effective control of power flows.Although conventional UPFC structures can be used to achieve this process,the expansion of power systems has led to the necessity of developing various UPFC devices.This paper focuses on an advanced real time control approach of UPFC for dynamic voltage regulation.The developed model is incorporated in the Gauss-Seidel(GS)power flow algorithm and the proposed method is validated on the IEEE-30 bus system that is designed under MATLAB/Simulink platform.As the proposed method was validated by comparing with the normal operating conditions,advantages were observed on two cases.In the first case,a generator outage is applied to system to observe behavior of proposed model in power loss conditions.In the second case,line fault conditions were used for observation.The results from testing the model for both cases prove that the approach has positive effects on dynamic power systems.

大规模风电并网后江苏电网柔直换流站与UPFC的有功功率协调控制方法

随着“双碳”战略的提出与实施,我国将着力建设以新能源为主的新型电力系统。然而,风电等新能源大规模并网将给具有交直流混联特征的新型电力系统带来威胁与挑战。通过以十四五规划末期的江苏电网为例进行分析,发现在大规模风电并网背景下,江苏电网中部分“南北向”500 kV交流输电线路N-1后负载过重的问题亟待解决。为此,基于综合灵敏度计算方法,提出了一种综合利用柔直换流站和统一潮流控制器的有功功率协调控制方法,用于改善系统潮流分布并消除潜在的线路过载。最后,以江苏电网为例进行了仿真分析,对苏州500 kV统一潮流控制器、白鹤滩-江苏直流和某规划中三端柔直换流站进行了有功协调控制。结果表明,所提协调控制方法应用于江苏电网时可有效解决交流输电通道N-1后负载过重问题,且相比于典型最优化方法在计算速度上具有优势。

基于改进类电磁机制算法的UPFC多目标优化配置

统一潮流控制器(UPFC)能在不改变线路拓扑结构的条件下有效地改善电力系统潮流,从而提高输电能力与电压稳定性。针对系统可用输电能力、电压偏差和L指标等目标,建立了UPFC的多目标优化配置模型,采用结合差分进化算法(DE)的改进差分类电磁机制算法(DEEM)对所建模型进行求解,通过对算法中粒子的带电量、合力计算方式进行改进,同时添加自适应因子,进一步平衡算法的全局搜索与局部搜索能力。配置后的结果表明UPFC对增强系统输电能力、电压质量及电压稳定性的性能均有提高,且改进算法寻优效率的提升也得到了验证。

基于MMC-UPFC-IPOD改善含风电系统功角稳定性

针对含风电系统功角稳定性问题,提出一个基于MMC-UPFC提高风电并网暂态功角稳定性的方法。利用Schauder固定点定理,将多输入多输出控制系统的合成和分析转化为一组等价的多输入单输出控制系统。将采用分散控制的H2/H∞应用到附加功率振荡阻尼控制中的附加改进功率振荡阻尼控制,以提高MMC-UPFC的输出特性,并在系统暂态时提高系统同步发电机的功角稳定性,并在仿真系统中验证了其有效性。

不平衡电网下MMC-UPFC的反演-滑模控制策略

针对模块化多电平变流器(MMC)-统一潮流控制器(UPFC)采用的控制方法存在的问题,本文提出了一种基于MMC-UPFC的反演控制(BSC)与滑模控制(SMC)组合而成的反演-滑模控制(BSC-SMC)非线性控制策略,这种控制策略既保留了SMC的抗干扰能力强等性能,也兼具BSC响应速度快等优点。首先,根据MMC-UPFC的拓扑结构,建立并联侧MMC变换器、串联侧MMC变换器的数学模型;其次,在不平衡条件下进行了正、负序分解,并设计了MMC-UPFC在不平衡条件下BSC-SMC控制器,并证明了控制系统的稳定性;最后,在MATLAB/Simulink软件平台搭建MMC-UPFC仿真模型进行仿真验证,通过把本文所提BSC-SMC控制策略与PID控制策略在接收端电源电压单相跌落、串联侧注入电压两种不同工况下进行了仿真比较,验证了BSC-SMC控制策略除具有SMC控制策略的抗扰性强特点外,还同时具有BSC控制策略的响应速度快和超调量小特点,且本文控制系统的稳定性更强、鲁棒性更好,从而验证了本文所提BSC-SMC控制策略的有效性和优越性。

低载波比调制下的MMC-UPFC电容电压减频效应

低载波比(载波频率与基波频率之比)的载波移相调制策略可有效降低MMC-UPFC的开关损耗,但会导致“减频效应”造成电容电压谐波频率明显降低,严重削弱电容电压均衡策略的控制效果。根据电容电压谐波频率随载波比降低的规律,定量分析了低载波比调制下MMC-UPFC电容电压的减频效应,明确了低载波比与电容电压低频波动、子模块电容不稳定充放电状态和子模块间电容电压不均衡间的内在联系及其发生机理;在此基础上,提出一种基于RBF神经网络的减频效应抑制策略,通过检测电容电压的谐波分量进行最优载波比选择和电容电压控制。最后以苏州南部500kV UPFC示范工程为参考进行仿真,证明了MMC-UPFC电容电压的减频效应的存在性以及抑制方法的有效性。

UPFC对风电场次同步谐振的抑制作用

随着风力发电机组容量的不断扩大,在有串联补偿输电线路的系统中,异步风力发电机存在引发次同步谐振的风险。统一潮流控制器(UPFC)在增强风电场系统稳定性的同时还能增加系统中的次同步阻尼,抑制风力发电机的次同步谐振。通过在桨距角控制中加入附加控制并改进UPFC的控制策略,产生相应的次同步阻尼转矩,达到抑制次同步谐振的目的。在IEEE第一模型中加入风电场模型和UPFC模型,仿真结果验证了文中提出的控制方法的有效性。

UPFC的潮流控制与暂态稳定性研究

从UPFC控制潮流的基本原理出发 ,详细地讨论了它对线路潮流的调节情况 ,建立了利用UPFC控制潮流的 3种优化模型 ,并针对UPFC对潮流的控制受功角变化的影响较大的特点 ,提出了一种有效的分段潮流控制策略 :根据暂态过程的不同阶段 ,相应地改变UPFC的控制方式 ,从而可大幅度地改善系统的暂态稳定性。单机无穷大系统的暂态仿真结果表明 :分段潮流控制策略是有效的。

基于直流侧电容电压弱控制策略的UPFC二阶段控制器设计

在分析常用直流侧电容电压控制方法的基础上,确定了直流侧电容电压强控制的概念,并相应地提出了直流侧电容电压弱控制策略。该策略能够利用UPFC直流侧电容吸收部分暂态能量,从而加速故障后线路上潮流稳定过程。基于直流侧电容电压弱控制的概念,结合线性最优控制方法,给出了相应的弱-强二阶段控制器设计实例及仿真结果。仿真实验表明,在系统发生三相对称短路故障时,该控制策略能够迅速地稳定被控线路的潮流和UPFC接入点的母线电压。该文提出的直流侧电容电压弱控制方式可与任一成熟的UPFC控制策略共同工作,以达到进一步改善控制效果的目的。

UPFC控制及动态特性实验研究

基于传统的比例—积分控制,提出了统一潮流控制器(unified power flow controller,UPFC)并、串联侧解耦的系统级控制策略,其控制目的是在并联侧维持UPFC并入点的交流电压和直流侧电容电压,在串联侧控制线路有功、无功潮流。文章首先介绍了所研制的UPFC实验系统平台,并在此基础上详细地给出了UPFC系统级控制器的硬件实现,实验平台的通用性决定了不同控制策略可以较容易地实现。为验证所提出的控制策略的控制效果,文中将UPFC实验装置嵌入至自行搭制的等效双机实验系统中,实验结果与PSCAD/EMTDC仿真环境下的时域动态仿真结果十分相似,从而得到了良好的UPFC动态特性。

基于PSASP的UPFC潮流控制建模与仿真

为了将统一潮流控制器UPFC(unified power flow controlle)r嵌入到商业软件中,采用节点注入电流法建立了UPFC的潮流控制模型。该模型通过控制UPFC串联侧节点的注入电流和并联侧节点的无功注入电流来控制线路潮流和UPFC接入点母线电压,其中,串联侧节点的注入电流通过功率目标方程直接求取,并联侧节点的无功注入电流通过引入被控母线电压的参考值与实际值的偏差求得。基于电力系统分析综合程序PSASP(power system analysis software package)进行了算例研究,结果表明所建模型能有效实现UPFC的潮流控制作用,且具有较快的潮流追踪速度和较高的收敛精度。对其他FACTS(flexible AC transmission system)器件的控制建模具有一定的参考价值。

UPFC的交叉耦合控制及潮流调节能力分析

研究了UPFC控制传输线路潮流能力,通过对系统功率平衡及UPFC的潮流控制特性分析,在三维空间中绘出了UPFC各部分的功率运行曲面,为有效选取UPFC各部分的功率容量和判断潮流控制方案的可行性提供了一个直观的手段,说明了在UPFC中采用交叉耦合控制的可行性。利用串联变换器注入传输线路电压的d轴分量控制传输线路上的无功潮流,用q轴分量控制传输线路上的有功潮流。控制系统设计中利用频率特性法得到了功率环PI调节器的参数。实验结果表明采用文中所述的控制策略能够使UPFC有良好的潮流调节性能。

UPFC状态反馈精确线性化潮流控制策略

统一潮流控制器(unified power flow controller,UPFC)传统线性控制器的性能可能因运行点的大范围变化而恶化,针对该问题提出了一种基于微分几何状态反馈精确线性化理论的UPFC非线性潮流控制策略。通过选择李雅普诺夫型输出函数、适当的非线性坐标变换和状态反馈将UPFC的5阶非线性系统完全转化为一个线性系统,然后采用线性极点配置方法设计了UPFC内部潮流控制器。IEEE 118节点系统的仿真对比结果表明,所提UPFC潮流控制策略改进了传统PI控制近似线性化的缺陷,有效适应了UPFC控制范围的大幅度变化,在提高电力系统暂态稳定性方面的效果明显优于传统PI控制。此外,该控制策略设计过程可以应用于所有基于电压源型换流器(voltage source converter,VSC)的柔性交流输电系统(flexibleAC transmission system,FACTS)装置。