A multi-objective approach to optimal placement and sizing of multiple active power filters using a music-inspired algorithm

This paper proposes a new multi-objective framework for optimal placement and sizing of the active power filters (APFs) with satisfactory and acceptable standard levels. total harmonic distortion (THD) of voltage, harmonic transmission line loss (HTLL), motor load loss function (MLLF), and total APFs currents are the four objectives considered in the optimization, while harmonic distortions within standard level, and maximum allowable APF size, are modeled as constraints. The proposed model is one of non-convex optimization problem having a non-linear, mixed-integer nature. Since, a new modified harmony search algorithm (MHSA) is used and followed by a min–max technique in order to obtain the final optimal solution. The harmony search algorithm is a recently developed optimization algorithm, which imitates the music improvisation process. In this process, the Harmonists improvise their instrument pitches searching for the perfect state of harmony. The newly developed method has been applied on the IEEE 18-bus test system and IEEE 30-bus test system by different scenarios and cases to demonstrate the feasibility and effectiveness of the proposed method. The detailed results of the case studies are presented and thoroughly analyzed. The obtained results illustrate the sufficiency and profitableness of the newly developed method in the placement and sizing of the multiple active power filters, when compared with other methods.     

电动汽车充电对电网的谐波影响研究

近年来,电动汽车产业发展迅猛,电动汽车相关技术已经成为研究焦点,电动汽车的规模化接入对电网的经济可靠运行以及电能质量问题越来越受到关注,谐波问题是电能质量影响的重要方面,首先通过对不同种类充电桩的MATLAB/Simulink建模研究单台充电桩引起的电压谐波分布及电压总谐波畸变,其次,对不同类型充电桩组成的充电站进行建模,并仿真分析在不同渗透率情况下对电网接入点的电压谐波影响情况,最后给出了电动汽车充电站建设中的几条建议。     

Optimal DG Allocation in Radial Distribution Systems with High Penetration of Non-linear Loads

This paper addresses the optimal distributed generation sizing and siting for voltage profile improvement, power losses, and total harmonic distortion (THD) reduction in a distribution network with high penetration of non-linear loads. The proposed planning methodology takes into consideration the load profile, the frequency spectrum of non-linear loads, and the technical constraints such as voltage limits at different buses (slack and load buses) of the system, feeder capacity, THD limits, and maximum penetration limit of DG units. The optimization process is based on the Genetic Algorithm (GA) method with three scenarios of objective function: system power losses, THD, and multi-objective function-based power losses and THD. This method is executed on the IEEE 31-bus system under sinusoidal and non-sinusoidal (harmonics) operating conditions including load variations within the 24-hr period. The simulation results using Matlab environment show the robustness of this method in optimal sizing and siting of DG, efficiency for improvement of voltage profile, reduction of power losses, and THD. A comparison with particle swarm optimization (PSO) method shows that the proposed method is better than PSO in reducing the power losses and THD in all suggested scenarios.     

A new arrangement of Z‐source AC–AC converter and its closed‐loop control system

In this study, a Z‐source alternating current‐to‐alternating current (AC–AC) converter with a specific topology, which can provide both buck and boost modes, is investigated. This converter, which can be implemented easily, utilizes only two switches with complemented commands. A comparison between the Z‐source AC–AC converter and a conventional thyristor voltage controlled one is presented here, and it shows that in the most areas, the Z‐source converter provides a faster response and lower total harmonic distortion of the output currents than the conventional one. Moreover, the Z‐source converter is also extended to the multiphase systems. In addition, a new arrangement of this converter is proposed here to remove the isolated single‐phase sources. Furthermore, an open‐loop method is proposed for soft‐starting applications. Finally, a closed‐loop control system is also suggested for a three‐phase Z‐source converter to soft start and control the speed of an induction motor. Computer simulations show the validity and effectiveness of the proposed schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

Realization of active power filter based on indirect current control algorithm using Xilinx system generator for harmonic elimination

Realization of active power filter with Model Based Design approach is presented in this paper. The approach adopts different modeling platforms as well as selection of proper hardware for step wise verification and testing. The active power filter model is developed using the Matlab/Simulink platform for single phase. The efficiency of the control algorithms such as synchronous detection method and indirect current control for active power filter is analyzed. Efficient control algorithm is developed by Xilinx system generator which is incorporated into Simulink as Xilinx tool box. Xilinx system generator provides a virtual platform for easy and effective design of the required system models in FPGA (field programmable gate array) design environments. Optimized automatic VHDL code is generated for the control algorithm which is simulated using ISE 13.2 for the generation of switching signals for the control of IGBTs of the active power filter. Suitable compensation signal is generated from the active power filter for the better elimination harmonics to improve the power quality. THD is reduced to a considered value which is able to satisfy the limits of the IEEE standard.     

A robust direct current control of DFIG wind turbine with low current THD based predictive approach

This paper presents a simple and robust direct current control based predictive approach for rotor side converter (RSC) of the doubly fed induction generator (DFIG), which operates at a constant switching frequency and has a fast dynamic response. First, sector of required rotor voltage vector is predicted in this strategy, and according to this predicted sector, two active vectors and two zero vectors are elected in each switching period. Derivatives of rotor current in the synchronous frame are determined for each predicted voltage vector in every period. These derivatives are used to compute the duration of the vectors in such a way that the current error at the end of the switching period gets minimized. The accuracy of the proposed control strategy under variation of rotor speed is evaluated in Matlab/Simulink environment for a 2 MW DFIG. Moreover, the impact of parameter variations on the system is examined for this suggested technique. Furthermore, the dynamic response and stator current total harmonic distortion (THD) of proposed strategy is compared with traditional vector control (VC), direct power control (DPC) and predictive direct power control (PDPC) methods. Finally, the performance of the proposed method is evaluated under disturbance voltage. The results demonstrate that suggested control technique has the lowest stator current THD and operates perfectly near the synchronous speed and under grid voltage dip. Copyright © 2015 John Wiley & Sons, Ltd.     

新型降压PFC与CRM升压APFC的性能比较研究

分析了一种新型降压PFC电路,并对比传统临界导电模式(CRM)升压APFC电路,通过仿真实验得到两种电路的性能参数.实验证明该新型降压PFC电路在低压小功率范围内较CRM升压电路有更高的效率,它使输出电压降到80 V以下,能有效抑制输出电压纹波,极大地减小了器件应力.但THD,PF值等参数明显劣于CRM升压电路,有待进...     

Multilevel inverter using cascaded 3-phase transformers with common-arm configuration

In multilevel inverter development for 3-phase applications, total number of transformer in the circuit can be reduced by using of cascaded 3-phase transformer circuit instead of single-phase transformer circuit. In the scheme, total number of switching components in the circuit is still a drawback to achieve lower cost and smaller size of the inverter compared with conventional multilevel inverter. This paper includes a challenging method to reduce total switching components in the multilevel inverter by adopting common-arm structure.The proposed inverter has been operated by two control schemes, Newton-Raphson and Equal-area method. After theoretical and experimental comparison of the methods, we found that Newton-Raphson method is useful to eliminate a specific harmonic order. However, the method has a shortcoming in real time operation which is performed by iterative calculation of the nonlinear equations. With Equal-area method, we can easily find the switching angles by calculating a trigonometric function. It can sufficiently minimize Total Harmonic Distortion (THD) of output voltage in real time operation of Digital Signal Processor (DSP).     

一种实用的谐波损耗计算方法

通过严格的推导得出了一种实用谐波损耗计算方法,该方法计算过程简单.所需数据可以直接从电能质量监测仪中得到,在基波损耗已算出的情况下,就可以准确的计算出谐波损耗.将谐波网损从管理线损中剥离出来,一方面理论线损计算更进一步接近真实值,有利于有效降损措施的提出;另一方面也为谐波污染治理提供了有力的手段.     

Single-stage sine-wave inverter for an autonomous operation of solar photovoltaic energy conversion system

This paper proposes a high performance single-stage inverter topology for the autonomous operation of a solar photovoltaic system. The proposed configuration which can boost the low voltage of photovoltaic (PV) array, can also convert the solar dc power into high quality ac power for driving autonomous loads without any filter. An MPPT circuit with parallel connection is implemented so that the part of the energy generated is processed by the dc–dc converter to supply dc loads. The line current total harmonic distortion (THD) obtained using this configuration is quite reasonable. The proposed topology has several desirable features such as low cost and compact size as number of switches used, are limited to four as against six switches used in classical two-stage inverters. In this paper analysis, simulation and experimental results are presented.