基于人工智能算法的电力系统无功优化调度研究

提出了一种自启发人工智能算法,以解决电力系统无功优化调度问题。该方法基于多变量优化理论,寻找实际发电量、发电机电压、分接变压器变比和无功补偿装置尺寸等控制变量的最佳组合,使网络总损耗最小。基于IEEE-30总线系统的25个变量对该算法进行了测试,并与3种现有算法进行了比较,验证了此算法的有效性,表明所提出的算法能高效实现最优化调度方案的制定。     

Hierarchical control strategy for a three-phase 4-wire microgrid under unbalanced and nonlinear load conditions

This paper proposes an improved hierarchical control strategy consists of a primary and a secondary layer for a three-phase 4-wire microgrid under unbalanced and nonlinear load conditions. The primary layer is comprised of a multi-loop control strategy to provide balanced output voltages, a harmonic compensator to reduce the total harmonic distortion (THD), and a droop-based scheme to achieve an accurate power sharing. At the secondary control layer, a reactive power compensator and a frequency restoration loop are designed to improve the accuracy of reactive power sharing and to restore the frequency deviation, respectively. Simulation studies and practical performance are carried out using the DIgSILENT Power Factory software and laboratory testing, to verify the effectiveness of the control strategy in both islanded and grid-connected mode. Zero reactive power sharing error and zero frequency steady-state error have given this control strategy an edge over the conventional control scheme. Furthermore, the proposed scheme presented outstanding voltage control performance, such as fast transient response and low voltage THD. The superiority of the proposed control strategy over the conventional filter-based control scheme is confirmed by the 2 line cycles decrease in the transient response. Additionally, the voltage THDs in islanded mode are reduced from above 5.1% to lower than 2.7% with the proposed control strategy under nonlinear load conditions. The current THD is also reduced from above 21% to lower than 2.4% in the connection point of the microgrid with the offered control scheme in the grid-connected mode.     

Nonlinear control of voltage source converters in AC–DC power system

This paper presents the design of a robust nonlinear controller for a parallel AC–DC power system using a Lyapunov function-based sliding mode control (LYPSMC) strategy. The inputs for the proposed control scheme are the DC voltage and reactive power errors at the converter station and the active and reactive power errors at the inverter station of the voltage-source converter-based high voltage direct current transmission (VSC-HVDC) link. The stability and robust tracking of the system parameters are ensured by applying the Lyapunov direct method. Also the gains of the sliding mode control (SMC) are made adaptive using the stability conditions of the Lyapunov function. The proposed control strategy offers invariant stability to a class of systems having modeling uncertainties due to parameter changes and exogenous inputs. Comprehensive computer simulations are carried out to verify the proposed control scheme under several system disturbances like changes in short-circuit ratio, converter parametric changes, and faults on the converter and inverter buses for single generating system connected to the power grid in a single machine infinite-bus AC–DC network and also for a 3-machine two-area power system. Furthermore, a second order super twisting sliding mode control scheme has been presented in this paper that provides a higher degree of nonlinearity than the LYPSMC and damps faster the converter and inverter voltage and power oscillations.     

基于虚拟仪器的平方检测法电压闪变测量实现

电压闪变已成为电力系统的重要污染,为实现闪变测量,简化了IEC推荐的平方检测法电压闪变测量过程,提出并建立了一种计算量小的基于Blackman窗插值FFr的平方检测法电压闪变测量算法,通过对离散的电压均方根值进行加窗插值FFT分解,求得电压均方根值的离散频谱数列U∫(j),对U∫(j)进行视感度加权处理,得到电压均方根值数列对应的瞬时闪变量p,进一步统计排序求得短时间闪变值Pst和长时间闪变值P(u).仿真实验验证了算法的可行性和准确性,在此基础上研制了基于虚拟仪器的电压闪变测量仪,给出了仪器构成与主框图程序,检验与运行证明了仪器的准确性.     

Fuel cell starvation control using model predictive technique with Laguerre and exponential weight functions

Fuel cell system is a complicated system that requires an efficient controller. Model predictive control is a prime candidate for its optimization and constraint handling features. In this work, an improved model predictive control (MPC) with Laguerre and exponential weight functions is proposed to control fuel cell oxygen starvation problem. To get the best performance of MPC, the control and prediction horizons are selected as large as possible within the computation limit. An exponential weight function is applied to place more emphasis on the current time and less emphasis on the future time in the optimization process. This leads to stable numerical solution for large prediction horizons. Laguerre functions are used to capture most of the control trajectory, while reducing the controller computation time and memory for large prediction horizons. Robustness and stability of the proposed controller are assessed using Monte-Carlo simulations. Results verify that the modified MPC is able to mimic the performance of the infinite horizon controller, discrete linear quadratic regulator (DLQR). The controller computation time is reduced approximately by one order of magnitude compared to traditional MPC scheme. Results from Monte-Carlo simulations prove that the proposed controller is robust and stable up to system parameters uncertainty of 40%.     

基于电压稳定临界状态分区的无功源配置

为解决无功功率不能远距离传输的问题,提出了在大电网电压稳定分区的基础上合理地配置无功源。首先,将分区点设定为电压稳定临界状态点,采用聚类分析的方法计算分区结果。然后,利用节点的无功裕度在电网拓扑中的分布,将各分区内无功裕度最小的节点作为无功源配置点。最后,采用Matlab软件对IEEE30节点系统进行了仿真,分别将所提方法与＂未分区、直接按照无功裕度大小配置＂的方法作比较。结果表明,该方法在应对临界状态时系统的无功控制更加可靠,故其对于提高系统电压的稳定性效果更好。     

A comparison of a novel robust decentralised control strategy and MPC for industrial high purity,high recovery,multicomponent distillation

In this work we have developed a novel, robust practical control structure to regulate an industrial methanol distillation column. This proposed control scheme is based on a override control framework and can manage a non-key trace ethanol product impurity specification while maintaining high product recovery. For comparison purposes, a MPC with a discrete process model (based on step tests) was also developed and tested. The results from process disturbance testing shows that, both the MPC and the proposed controller were capable of maintaining both the trace level ethanol specification in the distillate (X_D) and high product recovery (β). Closer analysis revealed that the MPC controller has a tighter X_D control, while the proposed controller was tighter in β control. The tight X_D control allowed the MPC to operate at a higher X_D set point (closer to the 10 ppm AA grade methanol standard), allowing for savings in energy usage. Despite the energy savings of the MPC, the proposed control scheme has lower installation and running costs. An economic analysis revealed a multitude of other external economic and plant design factors, that should be considered when making a decision between the two controllers. In general, we found relatively high energy costs favour MPC.     

Delay-tolerant distributed voltage control for multiple smart loads in AC microgrids

With increasing penetration of variable loads and intermittent distributed energy resources (DERs) with uncertainty and variability in distribution systems, the power system gradually inherits some features (e.g., lack of rotating inertia), which leads to the voltage instability in microgrids. As a means to provide stability support for smart grid against high penetration of intermittent DERs, inverter-based smart loads across the distribution grid has been suggested recently. Accordingly, this paper presents a delay-tolerant distributed voltage control scheme based on consensus protocol for multiple-cooperative smart loads through effective demand-side management in ac microgrids, in which the time-delay effect on transmission communication occurred in information exchanges is considered. The proposed distributed voltage control scheme always enables the output voltage of each smart load to be synchronized to their reference value, which improves the robustness of system stability against transmission communication delays. The Lyapunov–Krasovskii functions are employed to analyze the stability of our proposed distributed control scheme, then the delay-independent stability conditions are derived, which allows some large communication delays. Moreover, the sensitivity analysis is developed to show how the time delay affects system dynamics in order to validate the robustness of proposed delay-independent stability conditions. Furthermore, a sparse communication network is employed to implement the proposed distributed control protocols, which thus satisfies the plug-and-play requirement of smart microgrids. Finally, the simulation results of an ac microgrid in MATLAB/SimPowerSystems are presented to demonstrate the effectiveness of the proposed control methodology.     

PI and fuzzy logic controllers for shunt Active Power Filter--a report

This paper presents a shunt Active Power Filter (APF) for power quality improvements in terms of harmonics and reactive power compensation in the distribution network. The compensation process is based only on source current extraction that reduces the number of sensors as well as its complexity. A Proportional Integral (PI) or Fuzzy Logic Controller (FLC) is used to extract the required reference current from the distorted line-current, and this controls the DC-side capacitor voltage of the inverter. The shunt APF is implemented with PWM-current controlled Voltage Source Inverter (VSI) and the switching patterns are generated through a novel Adaptive-Fuzzy Hysteresis Current Controller (A-F-HCC). The proposed adaptive-fuzzy-HCC is compared with fixed-HCC and adaptive-HCC techniques and the superior features of this novel approach are established. The FLC based shunt APF system is validated through extensive simulation for diode-rectifier/R-L loads.     

A distributed model predictive control based load frequency control scheme for multi-area interconnected power system using discrete-time Laguerre functions

This paper proposes a distributed model predictive control based load frequency control (MPC-LFC) scheme to improve control performances in the frequency regulation of power system. In order to reduce the computational burden in the rolling optimization with a sufficiently large prediction horizon, the orthonormal Laguerre functions are utilized to approximate the predicted control trajectory. The closed-loop stability of the proposed MPC scheme is achieved by adding a terminal equality constraint to the online quadratic optimization and taking the cost function as the Lyapunov function. Furthermore, the treatments of some typical constraints in load frequency control have been studied based on the specific Laguerre-based formulations. Simulations have been conducted in two different interconnected power systems to validate the effectiveness of the proposed distributed MPC-LFC as well as its superiority over the comparative methods.     

Predictive control strategies for wind turbine system based on permanent magnet synchronous generator

In this paper, Model Predictive Control and Dead-beat predictive control strategies are proposed for the control of a PMSG based wind energy system. The proposed MPC considers the model of the converter-based system to forecast the possible future behavior of the controlled variables. It allows selecting the voltage vector to be applied that leads to a minimum error by minimizing a predefined cost function. The main features of the MPC are low current THD and robustness against parameters variations. The Dead-beat predictive control is based on the system model to compute the optimum voltage vector that ensures zero-steady state error. The optimum voltage vector is then applied through Space Vector Modulation (SVM) technique. The main advantages of the Dead-beat predictive control are low current THD and constant switching frequency. The proposed control techniques are presented and detailed for the control of back-to-back converter in a wind turbine system based on PMSG. Simulation results (under Matlab-Simulink software environment tool) and experimental results (under developed prototyping platform) are presented in order to show the performances of the considered control strategies.     

Adaptive super-twisting sliding mode control for a three-phase single-stage grid-connected differential boost inverter based photovoltaic system

This paper presents an adaptive super-twisting sliding mode control (STC) along with double-loop control for voltage tracking performance of three-phase differential boost inverter and DC-link capacitor voltage regulation in grid-connected PV system. The effectiveness of the proposed control strategies are demonstrated under realistic scenarios such as variations in solar insolation, load power demand, grid voltage, and transition from grid-connected to standalone mode etc. Additional supplementary power quality control functions such as harmonic compensation, and reactive power management are also investigated with the proposed control strategy. The results are compared with conventional proportional-integral controller, and PWM sliding mode controller. The system performance is evaluated in simulation and in real-time.     

配电网电压偏差治理措施对比分析

针对复杂配电网存在的距离大负荷输电导致的电压降低和水电丰期无功富余导致的电压抬升问题,选取了既有水电上网又有大负荷的复杂配电网作为分析对象,利用电力系统分析综合程序PSASP建立了问题稳态分析模型,对不同类型治理措施的配网电压偏差抑制效果进行了仿真。选取了分析对象实际运行时存在的3种典型潮流模式,分别采用无功集中补偿、分布式动态无功补偿和分布式固定无功补偿3种配网电压偏差治理措施,比较了3种无功治理措施的有效性和经济性,提出了不同形式无功补偿措施在配网电压偏差治理中的适用范围。研究结果表明:无功集中补偿措施适用范围有限,分布式无功补偿措施适用性强但经济型较差,对于电压偏差要求不高的配网可采用分布式固定无功补偿。     

TSC无功补偿控制策略研究及仿真分析

针对工厂中负载功率因数较低、电网向负载传输的无功功率较大,而导致电网电能损耗增大,电网电压不稳定的问题,对TSC动态无功补偿的原理和传统控制策略的弊端进行了研究,对基本控制策略、九域图控制策略、模糊控制策略进行了归纳,提出了一种基于模糊控制的改进型九域图无功补偿模糊控制策略,利用Matlab构建仿真模型,对用电负荷大小和功率因数发生突变时改进型控制策略的实时监测和控制性能进行了仿真。研究结果表明,以晶闸管投切电容器作为无功补偿方式的改进型无功补偿控制策略能实时快速地监测电网状态变化,并精准完成电容器投切动作,电网参数在一个电压周期内调整完毕并趋于稳定,功率因数波动幅度小,无过补偿,无投切振荡,系统反应迅速灵敏。     

弹性连杆机构振动的模型预测主动控制研究

基于机构离散状态空间模型,提出了抑制弹性连杆机构振动响应的模型预测主动控制方法。将复杂机构动力学模型中的非线性因素、耦合因素以及系统高阶模态的影响作为扰动,建立了预测机构动态变形响应的预测模型,采用带实时预测误差修正的模型预测控制方法对弹性连杆机构的振动进行了主动控制,降低了控制方法对复杂机构数学模型的要求,提高了控制系统的实时性。数值仿真和实验结果证明了该方法的有效性。     

Grouped-neural network modeling for model predictive control

A group of feed-forward neural networks (NNs), each providing the prediction of an individual process output at a future step, is used as the dynamic prediction model for the model-based predictive control (MPC) scheme in the proposed work. These NNs are parallel (independent) rather than cascaded--they are trained and implemented in parallel. Therefore, the complexity and effort in the training stage is decreased and compounded error propagation is eliminated from the prediction. A new strategy of compensating for the process-model mismatch under this grouped-NN model structure is also developed. Effectiveness of the scheme as a general nonlinear MPC is demonstrated by simulation results.     

静止无功发生器SVG的VF-DPC控制策略

针对静止无功发生器(SVG)传统电流控制方式输出谐波较多、电流响应速度慢的问题,介绍了静止无功发生器的工作原理及运行特性,提出了一种基于虚拟磁链定向的直接功率控制策略(VF-DPC),以瞬时功率与给定功率的计算差值为依据,在设计中采用双滞环结构的思路对电压矢量扇区内开关表进行改进,将差值送入开关表选取矢量,并以整流器开关的模式实现了系统控制。同时运用Matlab/Simulink工具,基于TSM320LF2812D型DSP的平台,对VF-DPC的补偿方案进行了仿真调试,将实验室搭建系统应用于冶金电网。研究结果表明,基于虚拟磁链定向的直接功率控制的静止无功发生器能够缩短补偿电流全动态响应时间,减小输出电流畸变量,且现场测试系统电网功率因数得到大幅提高,输出电压电流相位相同,完全满足系统无功补偿控制要求。     

Solid-state transformer-based new traction drive system and control

A new type of traction drive system consisting of solid-state traction transformer (SSTT), inverter unit, auxiliary inverter, traction motor and other key components is built in order to suit the demand of developing the next-generation electric traction system which will be efficient and lightweight, with high power density. For the purpose of reducing system volume and weight and improving efficiency and grid-side power quality, an efficient SSTT optimized topology combining high-voltage cascaded rectifiers with high-power high-frequency LLC resonant converter is proposed. On this basis, an integrated control strategy built upon synchronous rotating reference frame is presented to achieve unified control over fundamental active, reactive and harmonic components. The carrier-interleaving phase shift modulation strategy is proposed to improve the harmonic performance of cascaded rectifiers. In view of the secondary pulsating existing in a single-phase system, the mathematical model of secondary power transfer is built, and the mechanism of pulsating voltage resulting in beat frequency of LLC resonant converter is revealed, so as to design optimum matching of system parameters. Simulation and experimental results have verified that the traction system and control scheme mentioned in this paper are reasonable and superior and that they meet the future application requirements for rail transit.     

有源电力滤波器数字控制系统的研究

对有源电力滤波器全数字化控制系统的总体方案进行了设计,并联电压型三相有源电力滤波器主电路直流侧电容电压保持恒定,同时输出电流跟踪指令电流信号,详细设计了过零同步信号产生电路,并且利用PWM控制信号直接控制开关器件的导通与关断.谐波电流检测采用了瞬时无功功率理论的检测方法.最后用Matlab对有源电力系统搭建了模型并且进行了仿真,仿真结果验证了谐波电流检测方法的有效性及控制方案的可行性,可以更好地实现动态抑制谐波和无功补偿,并且整体设计精简了外设,能实现更多的控制算法.