Hysteresis current control technique of VSI for compensation of grid-connected unbalanced loads

The global trends nowadays in the power generation industry are to supplement the electricity production using distributed generation (DG) technologies based on renewable energy resources such as photovoltaic, wind power, etc. However, failure to properly control the operation of distributed energy resources as they connect to the exiting power grid could provoke many power quality problems on the grid side. For this reason, due considerations must be given to power generation and safe running before DG units is actually integrated into the power grid. The main aim of this paper is to address the grid interconnection issues that usually arise as DG units connect to the electric grid. The proposed strategy, implemented in Matlab/Simulink environment in different operating scenarios, provides compensation for active, reactive, unbalanced, and harmonic current components of grid-connected nonlinear unbalanced loads. The simulation results obtained in this study demonstrate the level of accuracy of the proposed technique, which ensure a balance in the overall grid phase currents, injection of maximum available power from DG resources to the grid, improvement of the utility grid power factor, and a reduction in the total harmonic distortion of grid currents.     

Modified Synchronous Vector Control Design of Multilevel Inverters for AC Grid Applications

This article presents a modified synchronous vector control design of a five-level cascaded H-Bridge inverter for integration of distributed generation (DG) resources to the power grid. The presented control strategy explores the limitations in the conventional synchronous vector control algorithm of grid-connected converter (GCC). The dynamic reference point (DRP) approach is considered to improve the performance of GCC. Compared with conventional control algorithm, DRP based control algorithm exhibits several specific advantages, such as increased reliability of the grid-interfaced converter, more active and reactive power injection capacity of the converter, and reduced cost of the converter. The objectives of control technique of the DG interface system are also employed to enhance the standard of the power grid. The optimized space vector pulse-width modulation (OSVPWM) control technique is used for grid integration. The simulation and experimental results are presented in order to validate the proposed functionalities of the grid-interfaced DG system. The effectiveness of the proposed control scheme is validated with better utilization of DG system, faster dynamics with reduced total harmonic distortion, better power factor, compensated load reactive power, and fault withstanding capability.     

Grid synchronization and control of distributed generation unit with flexible load compensation capabilities using multi-output LMS-filter

This paper deals with grid synchronization and control of single-phase voltage source inverter in distributed generation (DG) systems using a multi-output adaptive filter. Besides the active power injection, the proposed control enables the inverter to compensate load harmonic and reactive currents based on the capacity of inverter. The currents to be compensated are obtained using a multi-output adaptive filter structure that operates on the principle of variable step size (VSS) least mean squares (LMS) algorithm. The main objective of VSS-LMS filter is to decompose the load current into harmonic and reactive current components and compute their RMS values. The currents extracted by the VSS-LMS filter are used in developing a flexible compensation based on load compensation factors. The load compensation factors are calculated based on the remaining capacity of the inverter and priority. Harmonic currents compensation is given first priority over the reactive currents. In addition to harmonic currents detection, the same VSS-LMS filter is used in developing a phase locked loop unit for synchronizing the inverter with fundamental point of common coupling (PCC) voltage. Synchronizing the DG inverter with fundamental PCC voltage would make the proposed control algorithm insensitive to grid voltage harmonics and frequency fluctuations. The feasibility and the efficacy of the proposed control algorithm are demonstrated using hardware-in-the-loop (HIL) based experiments.     

新型混合有源电力滤波器的特性分析和控制方法

本文针对某变电站35kV高压侧存在谐波超标、无功不足的情况,研究了一种适用于高电压等级的大功率双谐振注入式混合有源电力滤波器。在分析了其拓扑结构的基础上,讨论了该滤波器的滤波性能特性、双谐振注入支路的无功补偿特性和其分压分流特性。为了增强整个系统的稳定性,提出了谐波电流双闭环控制策略,内环以逆变器输出电流为控制目标采用传统PI控制器;外环以电网谐波电流为控制目标,针对外环控制目标为非直流量的特性,提出了基于改进PSO-BP神经网络的递推积分PI控制方法,使用改进的PSO-BP神经网络来调整控制器的比例、积分系数,具有很好的稳态和动态性能。实例分析验证了本文研究内容的有效性和正确性。     

并联混合型有源电力滤波器的建模

为准确分析有源滤波器的运行特点,根据系统控制策略的需要,在考虑了有源滤波器输出的基础上采用开关函数法建立了并联混合型有源电力滤波器的数学模型,这样可推导出装置在系统中电压与电流的关系用于控制信号的产生。实践表明通过采用这种方法建立的模型对有源滤波器的滤波效果比较明显。     

三相四线制有源电力滤波器的一种新控制方法

提出了一种不对称非线性负载电路的动态补偿原理。运用该补偿原理,构建了三相四线制系统下的仿真模型,进行验证。仿真结果表明,在三相四线制系统中,该控制原理能对不平衡、非线性系统进行动态补偿。采用该控制方法控制已有的有源电力滤波器,测得的电网电流谐波含量明显减小。     

集中补偿型LCL-APF的有源阻尼控制方法研究

针对电网中采用无源网络进行滤波后仍然存在的谐波及无功问题,采用LCL-APF系统在变配电所侧对电网中的谐波及无功分量进行集中补偿。该LCL-APF系统采用直接功率控制的策略,省去了复杂的谐波检测及计算环节,改善了网侧电流的失真情况,将电网电流的谐波畸变率从26.86%降到了3.78%。通过机理建模及波特图分析,在功率控制环内加入有源阻尼环节,有效抑制了三相LCL系统引起的谐振问题,提升了LCL-APF系统的动态性能。仿真结果证明了该控制方法的正确性与可行性。     

单相整流负荷谐波功率需求建模分析

单相整流负荷作为典型的谐波源会对电网产生谐波污染,引起附加的谐波功率损耗。基于单相整流负荷工作原理,分析其各次谐波有功和无功功率流向特点,分别建立单相不控和相控整流负荷的功率需求模型。该模型计及整流器端电压和电流各次谐波分量之间的耦合关系,实现了整流负荷谐波功率的精确计算。利用仿真分析验证了该模型推导的正确性,并进一步定义了谐波有功和无功功率导纳矩阵。通过分析矩阵元素物理意义和幅值变化规律,确定单相整流负荷端电压各谐波分量对谐波功率的贡献程度。     

随机负载条件下非接触供电系统的自适应调谐方法

建立了基于可分离变压器的感应耦合电能传输系统的物理模型,从理论上研究了传输效率的影响因素。数学分析表明,动态负载会导致电路系统的电抗发生改变,因此系统会偏离谐振状态。提出了采用固定激励电源频率与动态调节电路无功器件参数相结合的方法进行自适应调谐。激励电源保持较高的固定工作频率,实时检测负载电流,根据最大电流原则调节回路的补偿电容值,使系统重新回归谐振状态。实验结果表明,所提方法能使系统重新回归谐振状态。     

新型注入式HAPF谐波电流及直流侧电压控制新方法

针对注入式混合有源滤波器中无源与有源部分补偿效果叠加、补偿谐波电流在经过注入支路和输出滤波器之后会产生一定的相位和幅值偏差,以及基波谐振支路的存在使得必须通过添加整流桥的方式获取直流侧电压从而难以保持直流侧电压的稳定等问题,提出了一种改进结构的新型谐振注入式混合型有源滤波器(hybrid active power filter,HAPF),使直流侧电容能够与电网产生能量交换。在此基础上结合提出的基于基波无功电流闭环调节的直流侧电压控制方法,保证了直流侧电压的稳定;提出了采用递推积分将无源滤波器作用后电网谐波电流与注入支路补偿电流进行闭环比较控制以获得参考电流的方法,减小了误差,提高了系统的控制精度。实验及仿真结果证明了所提出控制方法计算量较小,在响应时间和控制精度上都具有一定优势,能够满足系统的要求。     

考虑负荷与分布式电源随机性的配电网无功优化*

考虑负荷与分布式电源(DG)的随机性,在满足配电网运行约束条件以及补偿器动作次数约束条件下,提出配电网日整体收益最大,综合考虑分布式电源投资和维护费用以及补偿器投入费用的无功优化模型。用网损降损率变化率作为补偿器动作的"动作阀",同时针对遗传算法(GA)在寻优过程中寻优速度慢的缺点,用精英保留策略遗传算法(ESGA)求解含DG配电网无功优化问题。IEEE33节点配电系统算例仿真结果表明所提方法能有效解降低网络损耗,实现配电网动态无功优化。     

Design and control of LCL filter interfaced grid connected solar photovoltaic (SPV) system using power balance theory

In this paper solar photovoltaic (SPV) system connected to the utility grid is designed and simulated. The utility grid and SPV system are coupled with current controlled voltage source converter (VSC) and LCL filter. The design of LCL filter, MPPT algorithm and power quality improvements are discussed and simulation results are shown for the performance analysis of grid-coupled PV system under different load condition. The system is controlled through power balance theory method. The principle behind the control implementation is to evacuate the solar power generated during the daytime and the reactive power demand for the load should be supplied by the PV. The grid coupled system consists of SPV system, dc–dc boost converter, maximum power point tracking (MPPT), voltage source converter (VSC), LCL filter, different loads and three phase utility grid. This system is capable of eliminating harmonic and load balancing by supplying unbalanced current from the PV as a compensator. The system is simulated with 10 kW SPV array using indirect current control scheme.     

大功率混合型APF用于大型冶炼厂谐波治理

为消除电力系统谐波及其巨大危害,根据大型冶炼厂谐波治理的特点,提出了一种新颖的拓扑结构-大功率混合型有源滤波器,它将串联谐振注入型有源滤波器与无源滤波器并联混合,由电容静态补偿无功功率,由有源和无源部分共同抑制谐波。实践证明该装置具有较好的滤波效果和一定的无功补偿能力。     

基于可控超导储能的波动负载补偿

提出了一种应用可控超导储能(SMES)装置对波动负载进行补偿的方法。它可以使电网输入的有功功率保持恒定,同时对负载的无功功率进行补偿以提高功率因数。为了有效地进行功率控制,SMES装置的变流器采用电流源型的拓扑结构并与负载并联连接,同时采用闭环控制方法以提高系统的动态性能。为减小交流电流谐波成分,采用了优化脉宽调制开关策略。最后给出了一套20kJ／15kW SMES装置的仿真和实验结果。     

有源电力滤波器稳态和动态特性分析

文中对有源电力滤波器(active power filter,APF)的多种拓扑结构和多种控制策略进行了分析研究,以控制负载谐波电流、电网谐波电流、滤波支路谐波电流、负载谐波电压4种基本控制策略为基础,对并联混合型APF、串联混合型APF以及APF与PF(power filter,PF)串联后并入电网等几种典型的APF结构进行稳态和暂态分析,为合理选择APF结构及其控制策略提供理论依据。文中给出了APF工作在稳态和动态时实验波形,验证了理论分析的正确性,所得到的结论对APF的结构选择和实际应用具有一定的指导意义。     

双谐振注入混合型有源电力滤波器特性

在分析双谐振注入混合型有源电力滤波器(Double Resonance Injection Hybrid Active Power Filter, DIHAPF)结构和工作原理的基础上,建立了DIHAPF的系统控制模型及包括控制器的电压型逆变器的数学模型。从无功功率静态补偿能力和谐波分压特性两方面分析了DIHAPF注入支路特性,同时研究了DIHAPF的系统稳定性和谐波补偿特性,着重探讨了并联谐振支路谐振频率对系统性能的影响,提出了注入支路谐振频率设计方法。将非线性负载等效为谐波电流源,在PSIM6.0软件平台搭建DIHAPF模型进行仿真验证,并通过6 kV实验样机进行了实验研究。仿真和实验结果证明了理论分析的正确性。     

一种基于单位功率因数控制的有源电力滤波器

为解决谐波污染、改善电能质量,采用基于单位功率因数的控制方法,提出了一种只需检测系统侧电流及逆变器直流电容电压,而无需实时检测、计算负载谐波电流,直接控制系统侧电流为与电网电压同相的标准正弦波的控制方法,其补偿电流的控制策略采用比例积分控制和三角波调制。按照H桥逆变器的单极性脉宽调制的主电路研制了一台高性能的5kVA单相有源电力滤波器实验样机。理论分析、仿真及实验结果证明该有源电力滤波器可同时实现补偿负载无功及谐波电流,控制简单且具有良好的动态性能。     

A Dynamic Reactive Power Control for DFIG Wind Turbines andIts Impacts on Distribution Protections

With the increasing penetration of distributed generations(DGs)into power grids,the fault ride-through ability of DG is attracting more and more attention.Recent grid codes require a DG to maintain its connection with the grid during grid faults and to play an active role in the recovery of grid voltage.This paper chooses the doublyfed induction generator(DFIG)as the typical wind turbine for study.Firstly,a dynamic reactive power control strategy is proposed to improve the fault ride-through characteristic of a DFIG.The contributions of a DFIG to the fault current under the dynamic reactive power control and the Crowbar control are analyzed and compared based on the mathematical expressions and control behaviors.The impacts of a DFIG under two control strategies on distribution protections are discussed.Studies show that although a DFIG under the dynamic reactive power control provides more fault current component than one under the Crowbar control,its impacts on distribution protections are acceptable.Finally,a 10kV distribution network with a DFIG is simulated in PowerFactory DIgSILENT.The simulation results prove the correctness of above theoretical analysis.     

一种新型的并联有源滤波器非线性解耦控制方法的研究

以谐波治理为研究目的,针对有源滤波器模型是存在强耦合、非线性、结构复杂的系统的问题,提出一种利用微分几何方法建立了三相并联型有源电力滤波器的仿射非线性模型,使谐波电流与直流侧电压实现解耦,且可以独立地对其分别控制。同时提出了当负载发生变化存在迟滞的动态补偿方法,该方法可以很好地补偿谐波,改善功率因数,提高电网的利用率。在控制方法上利用仿射模型线性化后控制主电路,与常见控制算法对比,发现总谐波畸变率(THD)明显降低。最后,利用matlab2010b平台仿真证明了整体思路的正确性和有效性,为实现有源滤波器装置提供了可行性分析。     

基于电感电流无差拍控制的三相并网逆变器

针对传统并网逆变器的电流矢量PI控制存在功率耦合问题,需要进行复杂的解耦控制,难以实现并网逆变器系统无稳态误差控制。为了解决这一问题,文章采用瞬时功率外环和电感电流无差拍内环的控制策略,推导了三相并网逆变器的离散数学模型,减少了大量坐标变换,简化了并网逆变器控制系统的设计。通过Matlab仿真结果表明,在并网电流发生变化时,该控制策略仍可以实现并网逆变器输出有功、无功的功率解耦,且并网逆变器的输出电流具有良好的动态跟踪性能,电流谐波含量较低,满足并网要求。