Analysis and Power Quality Improvement in Hybrid Distributed Generation System with Utilization of Unified Power Quality Conditioner

This paper presents a comprehensive study that includes the sizing and power flow by series and parallel inverters in a distributed generation system(DGs)that integrates the system of hybrid wind photovoltaic with a unified power quality conditioner(UPQC).In addition to supplying active power to the utility grid,the system of hybrid wind photovoltaic functions as a UPQC,compensating reactive power and suppressing the harmonic load currents.Additionally,the load is supplied with harmonic-free,balanced and regulated output voltages.Since PVWind-UPQC is established on a dual compensation scheme,the series inverter works like a sinusoidal current source,while the parallel inverter works like a sinusoidal voltage source.Consequently,a smooth alteration from interconnected operating modes to island operating modes and vice versa can be achieved without load voltage transients.Since PV-Wind-UPQC inverters handle the energy generated through the hybrid wind photovoltaic system and the energy demanded through the load,the converters should be sized cautiously.A detailed study of the flow of power via the PV-Wind-UPQC is imperative to gain a complete understanding of the system operation and the proper design of the converters.Thus,curves that allow the sizing of the power converters according to the power flow via the converters are presented and discussed.Simulation results are presented to assess both steady state and dynamic performances of the grid connected hybrid system of PV-Wind-UPQC.This investigation is verified by simulating and analyzing the results with Matlab/Simulink.

非隔离单相半桥UPQC直流纹波分析及其影响抑制

非隔离单相半桥统一电能质量调节器(UPQC)两侧变换器的脉动功率差将在直流电容及分电容上产生复杂的多倍频电压纹波,各次电压纹波会对串联侧变换器的补偿电压有不同的影响,降低串联侧变换器的补偿效果。为了抑制直流电压纹波影响,利用等效电容电流模型计算直流电容电压表达式,分析直流纹波及非线性负载对补偿电压的影响路径,并仿真验证其正确性。针对分电容电压纹波和非线性负载对电压补偿效果的影响,提出一种抑制多倍频纹波影响的补偿电压特定次谐波控制策略。最后,基于SiC器件建立了非隔离单相半桥UPQC实验平台进行实验验证,实验结果表明在非线性工况下,所提控制策略将补偿电压THD从12.2%降低至2.4%,相比于传统控制可以减少约70%的直流电容需求。

基于FCS MPC的TNPC UPQC补偿策略研究

针对传统统一电能质量控制器(UPQC)控制策略存在控制性能不佳的问题,以三电平变流器为对象提出基于有限集模型预测控制(FCS MPC)的TNPC UPQC的补偿策略。设计了补偿量检测环节,研究了串并联侧补偿量控制策略;并通过进一步优化分区,在减少控制器计算量的同时,兼顾了三电平变流器中点电位平衡的控制效果。最后在MATLAB/Simulink仿真实验平台搭建模型,仿真结果证明了所提出的设计方法的正确性和可行性。

基于五桥臂MMC-UPQC的复合模型预测控制研究

针对模块化多电平统一电能质量调节器(modular multilevel unified power quality conditioner, MMC-UPQC)六桥臂结构下的单相桥臂故障问题,提出了一种五桥臂拓扑,这种新型拓扑可实现故障情况下的电能质量补偿。首先,对MMC-UPQC串并联侧的数学模型进行分析,提出了一种复合模型预测控制(hybrid model predictive control,H-MPC),所提控制方法结合了有限集模型预测控制(finite-control-set model predictive control, FCS-MPC)以及快速模型预测控制(fast model predictive control, F-MPC)。然后,通过构建两侧独立的价值函数减少了控制方法的计算量,同时也实现了五桥臂解耦控制。最后,相比传统线性(例如PI)和非线性(例如无源控制passivity-based control,PBC)的控制策略,所提复合模型预测控制在电压补偿、负序电压抑制以及谐波电流补偿等方面具有一定优势,并在一定程度上避免了复杂的参数整定及坐标变化环节。仿真实验结果证明了所提控制方法的可行性和优越性。

面向脉冲负载的基于超级电容储能UPQC设计及控制策略研究

针对带有脉冲负载电网的电压畸变和电流畸变问题,设计了带有超级电容储能的三电平统一电能质量调节器,提出了基于人工神经网络的方法对串联和并联补偿单元进行控制,基于双闭环PI控制的方法对超级电容储能单元进行控制。其中,串联补偿单元进行电压补偿,以维持负载电压的稳定,保证负载的用电需求;并联补偿单元进行电流补偿,以维持电源电流的稳定,避免电网受到持续大幅冲击;超级电容储能单元对直流侧进行充放电,以维持直流侧电压的恒定,保证串、并联侧的正常工作。所提方法省去了繁琐的坐标变换过程,避免了多个滤波器造成相位滞后的问题。仿真实验结果表明,所提拓扑和控制策略有助于改善带有脉冲负载电网的电能质量。

Unified power quality conditioner based on a three-level NPC inverter using fuzzy control techniques for all voltage disturbances compensation

This paper presents a novel and efficient control scheme for unified power quality conditioner （UPQC） based on three-level neutral point clamped （NPC） inverter using fuzzy logic techniques. The proposed UPQC is capable of mitigating source current harmonics and compensate all voltage disturbances such as voltage sags, swells, unbalances and harmonics. It is designed by the integration of series and shunt active filters （AFs） sharing a common DC bus capacitor. The DC voltage is maintained constant using proportional integral voltage controller. The synchronous reference frame （SRF） theory is used to get the reference signals for shunt active power filters （APFs） and the power reactive theory （p-q theory） for series APFs. The shunt and series APF reference signals derived from the control algorithm and sensed signals are injected in two controllers to generate switching signals. To improve the UPQC capability, fuzzy logic techniques are introduced to control the series APF. The performances of the proposed UPQC system are evaluated in terms of power factor correction, mitigation of voltage or current harmonics and all other voltage disturbances compensation using Matlab-Simulink software and SimPowerSystem toolbox. The simulation results illustrate the performance of the proposed UPQC at the common connection point of the nonlinear load to improve the power energy quality.

Voltage sag compensation strategy for unified power quality conditioner with simultaneous reactive power injection

Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC(namely UPQC-SRI) is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI(also called UPQCSRI region) is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.

基于有限集模型预测控制的UPQC预测直接控制策略

针对统一电能质量调节器(unified power quality conditioner,UPQC)线性控制算法中存在的控制结构复杂、控制器参数整定困难以及控制延时等问题,提出一种基于有限集模型预测控制(finite control set model predictive control,FCS-MPC)的UPQC预测直接控制策略。在分析UPQC直接控制系统构成基础上,基于FCS-MPC基本原理,实现了同步旋转坐标系下UPQC的有限集模型预测直接控制系统建模,有效简化了控制器结构,降低了控制算法的复杂度;基于UPQC系统有功功率平衡以及负载基波电压幅值恒定原控制器参数整定困难以及控制延时等问题,提出一种基于有则,建立了适用于UPQC串联侧与并联侧预测直接控制策略的给定值产生机制;最后,采用Matlab/Simulink仿真软件将所提控制策略与传统线性控制算法进行了对比仿真,并基于DSP (digital signal processor)(10)FPGA (field programmable gate array)(10)TYPHOON HIL402实验平台进行了实验验证,仿真与实验结果验证了所提控制策略的有效性和可行性。

Comprehensive control for unified power quality conditioners

This paper presents a comprehensive control strategy for unified power quality conditioners(UPQCs) to compensate for both voltage and current quality problems.The controllers for the series and shunt components of the UPQC are, equally, divided into three blocks: à main controller, which deals with the fundamental-frequency issues such as active and reactive power flow;` harmonic controller, which ensures zero-error tracking while compensating voltage and current harmonics;′ the set-point generation block, which handles the different control objectives of the UPQC. The controller design procedure has been simplified to the selection of three parameters for each converter. Furthermore, the proposed strategy can be implemented measuring only four variables, which represents a reasonable number of sensors. In addition, a pulse width modulation(PWM)-based modulation with fixed switching frequency is used for both converters. The proposed control strategy has been validated experimentally under different conditions, including grid-frequency variations.

Superconducting Magnetic Energy Storage Based DC Unified Power Quality Conditioner with Advanced Dual Control for DC-DFIG

The development of DC custom power protection devices is still in infancy that confines the sensitive loads integrated into medium-voltage(MV) and low-voltage(LV) DC networks. Considering the DC doubly-fed induction generator(DCDFIG) based wind energy conversion system(WECS), this paper proposes a dual active bridge(DAB) based DC unified power quality conditioner(DC-UPQC) with the integration of superconducting magnetic energy storage(SMES) to maintain the terminal voltage of DC-DFIG and regulate the current flow. The principle of the proposed DC-UPQC has three parts, i.e., parallel-side DAB(PDAB), series-side DAB(SDAB), and SMES,used for the voltage compensation, current and power regulation, and energy storage, respectively. The circuit principle of the PDAB and SDAB and the modeling of SMES are analyzed in this paper. A DC dual control strategy is also proposed to deal with the DC voltage oscillation generated by the AC-side asymmetrical fault. A case study of DC-DFIG interfaced with DC power grid is carried out, integrated with the proposed SMES-based DC-UPQC to verify the high-power applications of the proposed structure. Finally, an experiment is implemented, and the results demonstrate the correctness of the theoretical analysis and the feasibility of the proposed structure.

EV charging station with cascaded low-pass filtering scheme-based control of unified power quality conditioner

This paper proposes a cascaded low-pass filter(CLPF)scheme for the control of a unified power quality conditioner(UPQC)installed for enhancing the power quality of an electric vehicle(EV)charging station.With the incorporation of UPQC,the EV charging station draws sinusoidal currents at unity power factor and the supply voltage is maintained at the nominal value at the charger input.In the CLPF scheme,theα-βcomponents of the load current are individually processed through a cascade connection of two LPFs to determine the corresponding fundamental orthogonal components.Based on thus determined components,the instantaneous and peak value and phase angle of the fundamental positive sequence component(FPSC)of the load current are computed.Similarly,the corresponding quantities related to the load and supply voltages are also computed with the CLPF scheme.With the computations related to the load current and supply voltage,the unit voltage templates(UVTs),power factor and fundamental active component(FAC)of the load current are calculated.For the control of shunt compensation,reference currents are generated based on the FAC of the load current and UVTs.Alternately,the control of series compensation is employed with the help of UVTs and peak amplitude of the FPSC of the load voltage.The performance of CLPF scheme-based extraction is compared with that of the earlier reported schemes through simulation and experimental studies.The performance comparison reveals a faster dynamic and more accurate steady-state response with the proposed scheme.The performance analysis of the proposed CLPF scheme-based control of a UPQC deployed at the EV charging station for different operating conditions demonstrates station operation with requisite reactive power compensation and mitigation of voltage sag/swell,and prevention of propagation of harmonic and unbalanced currents into the grid.This results in increased reliability of charger operation,energy savings and increased efficiency of the distribution network.

The Full Load Voltage Compensation Strategy in Capacity Configuration of UPQC Integrated PV-BESS

Unified power quality conditioner(UPQC)with energy storage is commonly based on conventional capacity configuration strategy with power angle control.It has problems such as phase jumping before and after compensation.DC-link cannot continuously emit active power externally.Therefore,this paper presents the compensation strategy of full load voltage magnitude and phase in capacity configuration of UPQC.The topology of UPQC is integrated a series active power filter(SAPF),a shunt active power filter(PAPF)and a photovoltaic-battery energy storage system(PV-BESS).The principle of full load voltage compensation is analyzed based on the PV-BESS-UPQC topology.Themagnitude constant of load voltage ismaintained by controlling the appropriate shunt compensation current.Then the UPQC capacity configuration is carried out using the full load voltage compensation strategy.The compensation capacity of UPQC series and shunt units are reduced.Finally,the simulation results show that the proposed compensation strategy reduces the capacity configuration by 5.11 kVA(36.4%)compared to the conventional compensation strategy.The proposed strategy can achieve full compensation of the load voltage,which can effectively reduce the capacity allocation and improve the economy of UPQC.It also has the PV-BESS units’ability of providing active power and can stabilize the DC-link voltage.

Multi-Level Inverter Linear Predictive Phase Composition Strategy for UPQC

The power system is facing numerous issues when the distributed gen-eration is added to the existing system.The existing power system has not been planned with flawless power quality control.These restrictions in the power trans-mission generation system are compensated by the use of devices such as the Static Synchronous Compensator(STATCOM),the Unified Power Quality Con-ditioner(UPQC)series/shunt compensators,etc.In this work,UPQC’s plan with the joint activity of photovoltaic(PV)exhibits is proposed.The proposed system is made out of series and shunt regulators and PV.A boost converter connects the DC link to the PV source,allowing it to compensate for voltage sags,swells,vol-tage interferences,harmonics,and reactive power issues.In this paper,the fea-tures of a seven-level Cascaded H-Bridge Multi-Level idea are applied to shunt and series active filter changeovers to reduce Total Harmonic Distortion and com-pensate for voltage issues.Despite its power quality capacity for common cou-pling,the proposed system can inject the grid’s dynamic power.During voltage interference,it can also provide a piece of delicate burden power.The simulation is carried out with the help of MATLAB/SIMULINK programming,and the results are compared to those of other conventional methods.

一种新型无差拍UPQC预测直接控制策略

针对统一电能质量调节器(unified power quality conditioner,UPQC)传统线性控制算法中存在多个PI控制器及PWM调制环节,导致系统参数整定困难、结构复杂的问题,提出一种新型无差拍UPQC预测直接控制策略。推导并建立同步旋转坐标系下UPQC串、并联侧预测直接控制模型;基于无差拍控制原理与有功功率平衡原则构建了串联侧给定电流产生机制,实现了直流侧电压的无差拍控制和网侧电流的预测直接控制;基于无差拍控制原理与负载侧电压恒定原则构建了并联侧给定电流产生机制,实现了负载侧电压的无差拍预测直接控制。仿真与实验分析结果表明,所提算法无PI和PWM调制环节,有效简化了控制系统结构,并提高了系统的动态性能及补偿效果。

基于超级电容器储能的UPQC工作条件及控制策略

为处理常规统一电能质量调节器(UPQC)难以解决的电源瞬时中断或电压暂降较深的问题,提出利用超级电容器储能系统(SESS)构成UPQC的直流储能单元。针对基于SESS的UPQC拓扑结构,研究UPQC单元优化配置的影响因素和目标函数,得出UPQC系统级功率流协调控制的最佳工作条件;分析SESS的主电路结构特点和性能,确定储能单元的容量和SESS控制策略;根据UPQC串、并联变流器的工作要求,提出基于PI控制和重复控制的UPQC单元级控制策略。仿真与实验分析结果表明,所提出的拓扑结构和控制策略在达到电能质量治理目标的同时,实现了UPQC串、并联变流器以及SESS协调控制。

UPQC切换运行模式的小信号分析及协调控制策略

针对统一电能质量调节器(UPQC)切换运行模式时引起的小扰动稳定性及动态交互影响问题,建立了包括串、并联变流器控制在内的小信号模型,对比分析了串、并联变流器独立运行以及联合运行时的稳定性及动态性能,并以特征根灵敏度的方法研究了控制参数、负荷等因素与UPQC运行模式切换时的小扰动稳定性的关联机理。该结论可为UPQC的参数设计提供部分参考依据,其后提出了可减少串并联变流器与电网之间能量交换、提高串联变流器利用率的新型功率流协调控制策略。时域仿真证实了相关结论的有效性及协调控制策略的可行性。

基于定有功电流限值控制的MMC型UPQC协调控制方法

对电压暂降期间MMC型UPQC串联侧补偿能力进行深入的理论分析。首先给出MMC型UPQC的工作原理,推导出暂降补偿幅值、补偿持续时间、主回路电气量及MMC参数之间关系的时域表达式;进而提出一种针对容量确定情况下UPQC串联侧过电流问题的协调控制设计方法,在传统定直流电压控制的基础上提出定有功电流限值控制;定义了划分MMC型UPQC处于上述两种控制状态的电压暂降临界值并给出数值计算表达式;最后PSCAD/EMTDC下的系统仿真结果验证了理论分析的正确性。仿真结果也表明,与传统协调控制方法相比,该文提出的协调控制方法可明显提高电压暂降的补偿幅值和持续时间。

面向配电网接地故障暂稳态协同调控的UPQC优化运行方法

针对现有有源消弧装置存在稳态时直流侧取电难、直流电容难以稳压,暂态时接地故障瞬时过电压等问题,充分解析了接地故障全过程中统一电能质量调节器(unified powerqualityconditioner,UPQC)主动参与调控的潜力,提出一种面向配电网接地故障暂稳态协同调控的UPQC优化运行方法。将使用此方法的装置简称为具备消弧功能的统一电能质量调节器(arcsuppression-unifiedpowerquality conditioner,AS-UPQC)。首先,通过分析消弧稳态模式下AS-UPQC系统的功率流向,提出一种适用于AS-UPQC的能量主动平衡方法,通过控制AS-UPQC串联侧从电网吸收一定的有功来补偿并联侧消弧时消耗的有功。该方法在无需额外储能设备的前提下,有效保证了消弧装置直流侧电容能量平衡。其次,对接地故障的暂态模式进行分析,提出一种暂态响应优化的控制方法。在发生接地故障瞬间,控制串联侧从电网中吸收的有功,其等效增大系统阻尼,加快暂态过渡过程,从而抑制瞬态过电压的幅值。最后,通过仿真和实验验证了所提调控方法的有效性与可行性。

UPQC直流储能单元的APFC控制技术

统一电能质量控制器(UPQC)是用户电力技术中的新兴装置,它能统一实现多重电能质量调节功能。系统地介绍了UPQC的综合补偿功能,并给出了一种典型的UPQC拓扑结构。为了进一步提高UPQC的性能,将有源功率因数校正(APFC)技术引入UPQC直流储能单元的直流电容电压控制,详细阐述了其工作原理,并给出了仿真实验结果。APFC技术用于UPQC的直流储能单元中是完全可行的,它使UPQC的性能更完善。

基于无功功率流的UPQC协调控制策略

针对统一电能质量调节器UPQC常规控制中,其串并联变流器功能相对独立、利用率低的问题,提出基于无功功率流的UPQC协调控制策略。应用所设计的UPQC系统结构,协调分配UP-QC串并联变流器的无功功率输出,控制串联变流器输出电压向量垂直相应的电流向量,控制并联变流器输出电流向量垂直相应的电压向量,有效消除了有功环流的影响。特别针对电网侧没有电能质量问题时,控制串联变流器继续输出无功功率,充分发挥两变流器的无功补偿功能。理论推导UPQC系统功率流的关系,并仿真实验分析提出的控制策略,结果表明该控制策略解决电能质量问题的同时,实现了UPQC串并联变流器功率的合理分配。