THD reduction with reactive power compensation for fuzzy logic DVR based solar PV grid connected system

Dynamic voltage restorer (DVR) is used to protect sensitive loads from voltage disturbances of the distribution generation (DG) system. In this paper, a new control approach for the 200 kW solar photovoltaic grid connected system with perturb and observe maximum power point tracking (MPPT) technique is implemented. Power quality improvement with comparison is conducted during fault with proportional integral (PI) and artificial intelligence-based fuzzy logic controlled DVR. MPPT tracks the actual variable DC link voltage while deriving the maximum power from a photovoltaic array and maintains DC link voltage constant by changing modulation index of the converter. Simulation results during fault show that the fuzzy logic based DVR scheme demonstrates simultaneous exchange of active and reactive power with less total harmonic distortion (THD) present in voltage source converter (VSC) current and grid current with fast tracking of optimum operating point at unity power factor. Standards (IEEE-519/1547), stipulates that the current with THD greater than 5% cannot be injected into the grid by any distributed generation source. Simulation results and validations of MPPT technique and operation of fuzzy logic controlled DVR demonstrate the effectiveness of the proposed control schemes.     

Power quality investigation of a solar PV transformer-less grid-connected system fed DVR

This paper presents a single stage transformer-less grid-connected solar photovoltaic (PV) system with an active and reactive power control. In the absence of active input power, the grid-tied voltage source converter (VSC) is operated in a reactive power generation mode, which powers the control circuitry, and maintains a regulated DC voltage to the VSC. A data-based maximum power point tracking (MPPT) control scheme which performs power quality control at a maximum power by reducing the total harmonic distortion (THD) in grid injected current as per IEEE-519/1547 standards is implemented. A proportional-integral (PI) controller based dynamic voltage restorer (DVR) control scheme is implemented which controls the grid side converter during single-phase to ground fault. The analysis includes the grid current THD along with the corresponding variation of the active and reactive power during the fault condition. The MPPT tracks the actual variable DC link voltage while deriving the maximum power from the solar PV array, and maintains the DC link voltage constant by changing the modulation index of the VSC. Simulation results using Matlab/Simulink are presented to demonstrate the feasibility and validations of the proposed novel MPPT and DVR control systems under different environmental conditions.     

考虑补偿方法的单相DVR检测方法研究与仿真

定量分析计算电网电压暂降时DVR逆变单元与电网的功率交换情况,详细研究逆变单元在各种补偿策略下的输出电压和有功功率与故障前后电网电压、负载电压和参考相量的具体关系,并根据具体关系总结出5种补偿方法,通过Matlab平台对各种补偿方法进行仿真研究,最后根据不同的补偿方式进行单相DVR检测方法研究。     

DFIG-DVR系统在不平衡电网电压下的运行特性

针对双馈风电机组(DFIG)在电网电压不平衡时,二倍频扰动分量会造成定转子过电流、功率脉动、转矩脉动等一系列电气和机械的问题,提出了新型DFIG-DVR系统,即串联DVR始终维持DFIG定子端电压恒定,从根源上隔离电网不平衡故障的影响,从而在整个故障运行过程中,DFIG仍可以实现转子侧变换器功率解耦控制和网侧变换器维持直流电压恒定的目标。采用PSCAD/EMTDC建立DFIG-DVR系统模型,对比分析了电网电压不平衡时DVR的不投切与投切对DFIG的影响。结果表明,在电网电压不平衡条件下,所提控制方案可以实现DFIG的平衡运行。     

Maximum power point tracking supported proton exchange membrane fuel cell based intelligent dynamic voltage restorer

In modern era, electrical power utilities are more concerned about power quality. In this endeavour, dynamic voltage restorer (DVR) provides adequate support to the system. Accordingly, the present work illustrates intelligent hybrid control mechanism for DVR. Artificial neural network (ANN) is incorporated to obtain real-time optimal gains under distinct voltage situations. Closed loop type 2 fuzzy logic (CLT2-FL) is also realized in order to assist the ANN supported unit concomitantly. In order to enhance the potential of the present DVR, a CLT2-FL controlled maximum power point tracking (MPPT) based proton exchange membrane fuel cell arrangement is also explored in the present study. CLT2-FL module is adopted in DC-DC converter topology to provide simultaneous supply to the loads at different and regulated voltage levels. Consequently, the results are evaluated and compared to the state-of-the-arts which unveil the efficacy of the implemented controller against the oddity seen in the voltage waveform, thereby, exhibiting better voltage regulation and less harmonics. The effectiveness of the implemented MPPT unit from the viewpoints of convergence speed and oscillations is also established.     

动态电压恢复器对微机保护影响的仿真研究

为了分析DVR对配电系统的影响,介绍了DVR的原理、结构,论述了DVR在配电系统的作用,接着针对DVR对微机电流保护中的影响做了仿真.仿真分析表明:DVR的接入使得配电系统电流保护的灵敏度提高,但使电流保护失去了选择性.针对这一问题,提出了解决方案,仿真结果验证了方案的正确性.     

Performance investigation of artificial intelligence based controller for three phase four leg shunt active filter

In this paper, the choice of power quality compensator is a DSTATCOM which constitutes a three phase four leg voltage source converter (VSC) with a DC capacitor. The control strategy proposed for the DSTATCOM is a neural network based one cycle control (OCC). This control strategy involves neural network block, digital circuits and linear elements, which eliminates the sensors required for sensing the load current and coupling inductor current in addition to the multiplier employed in the conventional method. The calculation of harmonic and reactive currents for the reference current generation is also eliminated, thus minimizing the complexity in the control strategy. The control strategy mitigates harmonic/reactive currents, ensures balanced and sinusoidal source current from the supply mains that are nearly in phase with the supply voltage, compensates neutral current, and maintains voltage across the capacitor under unbalanced source and load conditions. The performance of the DSTATCOM with the proposed artificial neural network (ANN) controllers is validated and investigated through simulations using Matlab software. The simulation results prove the efficacy of the proposed neural network based control strategy under varying source and load conditions.     

基于幅值的电压暂降特征量检测方法

分析了现有的电压暂降检测方法,提出了基于幅值的电压暂降特征量检测新方法。该方法通过低通滤波器、根锁相和开平方等环节可快速推导出暂降基波电压的幅值,然后根据暂降基波电压幅值快速推导出相位跳变角。与DVR装置中广泛采用的瞬时电压dq分解法比较,该方法的延时明显减少,可以对电压暂降的特征量进行迅速、准确判断。MATLAB仿真结果证明了该方法的有效性。     

Operation and control of dynamic voltage restorer using single-phase direct converter

In this paper, a new topology based on a direct ac/ac converter is proposed for a single-phase dynamic voltage restorer (DVR). This topology uses the minimum switches (i.e. two switches) and does not require dc-link energy storage elements. As a result of elimination of the energy storage elements, the cost and the physical size of the proposed topology is reduced. A new control method is also proposed for direct ac/ac converter in the proposed topology. The proposed topology is properly able to compensate voltage sag and swell in the desired range according to the turn ratio of the injection transformer and is also able to eliminate harmonics and flickers. Considering these capabilities, the proposed topology is a several purpose device with a simple topology. It is worth noting that all of these capabilities are not integrated in the conventional DVR topologies. It is obvious that the proposed topology would not face any problems in long time compensation due to the fact that it provides the required energy directly through the grid. The proposed topology can be easily extended to n-phase systems such as three-phase based on the same principle of the operation. In n-phase systems, the voltage sags and swells can be properly compensated regardless of the balanced or unbalanced operation. The experimental and simulation results are presented to validate the capabilities of the proposed topology.     

基于遗传算法的动态电压恢复器不对称暂降补偿方法

电压暂降作为一种电能质量问题,由于不对称故障的存在,使处理不对称电压暂降变得复杂。电压暂降除了幅值减小外,还往往伴随着相角跳变,这样更增加了补偿难度。电压暂降发生幅值不对称和相角不对称,都对电子变流设备有着严重的影响,因此需要将负荷电压的幅值恢复到容忍范围,同时保持三相电网电压对称。由于动态电压恢复器(DVR)受最大注入电压限制,需要建立一种方法使DVR的各相注入电压得到有效控制。针对动态电压恢复器(DVR)补偿电压约束下,不对称故障电压补偿,采用遗传算法对其注入电压实施控制,并以算例说明该方法的有效性。     

光伏并网逆变器辅助电源设计

太阳能是清洁安全可靠的可再生能源,采用光伏并网技术的太阳能发电已成为应用面最广的光伏新能源应用技术。基于电流型PWM控制芯片UCC2801设计了一种光伏并网逆变器用辅助电源,采用4路输出的单端反激式拓扑,由光伏并网逆变器的直流母线供电,并采用电压基准源及光耦实现隔离反馈。试验结果表明,该辅助电源输入电压范围宽、输出纹波小、交叉负载调整率低,还能防止反复启停及在电源启动后自动关断。     

基于无源控制策略的MMC-DVR控制系统

为了提高高压电网电压质量补偿效果,提出基于模块化多电平换流器（MMC）的动态电压调节器（DVR）系统的无源非线性控制方法。首先,介绍MMC-DVR的框图以及工作原理,根据基尔霍夫电压电流定律,分别构建abc静止与两相dq旋转坐标系下的数学模型;接着提出无源控制方法来解决问题;最终,在Matlab/Simulink软件实验平台上构建MMC-DVR系统,构建仿真验证无源非线性控制的可行性和优越性。与传统PID相比,无源策略能使系统迅速稳定,提高抗扰能力,采取阻尼注入,能快速、有效地对电压降落/升高和谐波进行补偿,并且无源非线性控制器控制规律简单,所需控制器数量少,可避免PI控制参数选择困难及繁复的缺点。     

The Control of Large Wind-Farm-Induced Voltage Fluctuations

The contemplated use of large sources of intermittent generation such as wind in concert with conventional utility generation poses special operational problems. These problems include the propensity of the wind-driven source for upsetting the voltage regulation systems. Related to voltage depression is the often excessive VAR requirements which lead to large network losses if not controlled. This paper explores the use of an AC/DC/AC interface designed to control these voltage related problems. An extinction angle control algorithm is proposed and simulation results are used to show the advantage of such control.     

Dynamic Voltage Restorer with Active Disturbance Rejection Control

Power quality is one of the major concerns among consumers and electric utility companies. CUPS （custom power systems） devices are used to improve the quality of power and enhance the reliability of the power supply in the distribution networks. The DVR （dynamic voltage restorer） is an important CUPS device used to mitigate voltage sag/swell and imbalances. Various control techniques have been implemented to control the DVR, among which the PID （proportional-integral-derivative） controller is dominant because of its model independent property and its error driven technique. In this paper, a new controller based on the ADRC （active disturbance rejection control） concept is developed, and its performance is compared to that of the PID controller. The model of the DVR and its ADRC and PID controllers were developed under the MATLAB （matrix laboratory）/Simulink environment. The simulation results demonstrated the effectiveness of the ADRC over the PID controller.     

级联式无刷双馈发电机的仿真研究

介绍了级联式无刷双馈发电机的结构和发电原理,根据异步电机的电压方程和坐标变换理论,推导出无刷双馈电机的转子机械速dq坐标系下的数学模型,并进行了Matlab建模和仿真.仿真结果验证了该数学模型的正确性,并为级联式无刷双馈变速恒频发电系统的进一步研究提供了理论基础.     

Virtual inductor-based islanding detection method for grid-connected power inverter of distributed power generation system

An islanding detection method is proposed for a distributed power generation system that comprises a DC power source and a grid-connected power inverter connected in parallel to the utility. Besides serving to generate the fundamental real power, the grid-connected power inverter also acts as a virtual inductor when the frequency is slightly higher than the fundamental voltage frequency of the utility. The distributed power generation system is the only source supplying power to the load when the utility is interrupted; consequently, the amplitude or frequency of the load voltage changes because of the operation of the virtual inductor. Hence, the proposed method can immediately detect the islanding operation. A prototype was developed and tested to demonstrate the performance of the proposed islanding detection method. Experimental results show that the proposed method can detect islanding operations effectively.     

计及风光系统出力随机性的电压风险评估

针对风力发电和光伏发电并网后改变系统潮流大小和方向并对电网电压产生影响的问题,建立了风电和光伏出力概率模型,并使用Monte Carlo方法模拟了实际风速和光照辐照强度的概率分布区间,进而计算了风电和光伏的随机出力,并结合风险理论考虑风光系统出力随机性对电网电压风险的影响。以IEEERTS79标准测试系统为例,评估了风光系统接入容量及风光发电系统容量配置比例对电网电压风险的影响。算例的评估结果可为风光系统接入容量大小和风光发电系统容量配置比例提供参考。     

Power quality improvement of solar photovoltaic transformer-less grid-connected system with maximum power point tracking control

This paper presents a transformer-less single-stage grid-connected solar photovoltaic (PV) system with active reactive power control. In the absence of active input power, grid-tied voltage source converter (VSC) is operated in the reactive power generation mode, which powers control circuitry and maintains regulated DC voltage. Control scheme has been implemented so that the grid-connected converter continuously serves local load. A data-based maximum power point tracking (MPPT) has been implemented at maximum power which performs power quality control by reducing total harmonic distortion (THD) in grid-injected current under varying environmental conditions. Standards (IEEE-519/1547) stipulates that current with THD greater than 5% cannot be injected into the grid by any distributed generation (DG) source. MPPT tracks actual variable DC link voltage while deriving maximum power from PV array and maintains DC link voltage constant by changing the converter modulation index. Simulation results with the PV model and MPPT technique validations demonstrate effectiveness of the proposed system.     

Energy management of fuel cell/battery/supercapacitor hybrid power source for vehicle applications

This paper proposes a perfect energy source supplied by a polymer electrolyte membrane fuel cell (PEMFC) as a main power source and storage devices: battery and supercapacitor, for modern distributed generation system, particularly for future fuel cell vehicle applications. The energy in hybrid system is balanced by the dc bus voltage regulation. A supercapacitor module, as a high dynamic and high power density device, functions for supplying energy to regulate a dc bus voltage. A battery module, as a high energy density device, operates for supplying energy to a supercapacitor bank to keep it charged. A FC, as a slowest dynamic source in this system, functions to supply energy to a battery bank in order to keep it charged. Therefore, there are three voltage control loops: dc bus voltage regulated by a supercapacitor bank, supercapacitor voltage regulated by a battery bank, and battery voltage regulated by a FC. To authenticate the proposed control algorithm, a hardware system in our laboratory is realized by analog circuits and numerical calculation by dSPACE. Experimental results with small-scale devices (a PEMFC: 500-W, 50-A; a battery bank: 68-Ah, 24-V; and a supercapacitor bank: 292-F, 30-V, 500-A) corroborate the excellent control principle during motor drive cycle.     

Apparatus for supplying an isolated DC load from a variable-speedself-excited induction generator

This paper describes the design and laboratory testing of novel generation apparatus for supplying an isolated DC load from a self-excited induction generator operable at variable speed. The variable-speed generating apparatus consists of a self-excited induction machine, a controlled Graetz bridge rectifier, a voltage-boost power converter, and a control system. The induction generator supplies the rectifier. The voltage-boost power converter interfaces the variable output voltage of the rectifier to the fixed DC voltage required for the load. The rectifier is operated at levels of average DC current and voltage which control machine voltage to the rated AC voltage and which also draw the necessary power to supply the DC load. Performance is enhanced with respect to earlier apparatus in that both the DC voltage supplied to the load and the AC voltage on the machine are simultaneously controlled to fixed reference levels over broad operating ranges of load and speed