Sensitivity evaluation and comparison for high-order active filters

This paper presents a systematic procedure for evaluating the sensitivity of the transfer function magnitude, and hence the transmission deviation in decibels, for high-order active filters. The procedure applies for filters having any arbitrary structure of coupled biquadratic sections. The method is illustrated by carrying out a comparative analysis on a bandpass filter realized by the Cascade, Leap-Frog and Primary Resonator Block approaches.     

Sensitivity analysis and dynamic range of quad filters and some comparative results

The paper considers general sensitivity analysis and dynamic range of quad filters. The use of quad structures in the design of symmetrical and/or unsymmetrical active filters is studied from the sensitivity and dynamic range points of view and these are compared with other design methods. Determination of gain constants of biquadratic blocks either according to overloading or noise immunity or both for quad realization are also considered. It is shown that, especially for symmetrical transfer functions, the design equations are simple and that the sensitivity performance is as good as the FLF and LF configurations and better than GFLF. Furthermore, it is shown with an example that quad realization also yields better dynamic range as compared to GFLF.     

Sensitivity of third- and higher-order filters

For any realization of a network function F(s) = N(s)/D(s), the sensitivities that can be most readily calculated are those of the coefficients in N(s) and D(s). A simple relationship is derived that enables one to calculate the root (pole and zero) sensitivities of F(s) in terms of the coefficient sensitivities. The root sensitivities, in turn, enable one to calculate the root pair Q and root frequency sensitivities, which can be used to characterize and compare different realizations of F(s). Application to 3rd- and 4th-order filters reveals formulations that are more elegant than those already known in the literature.     

新型直流侧串联型有源电力滤波器

针对广泛应用的整流类负荷的谐波治理,提出一种单相输出电压可调的新型直流侧有源电力滤波器.从理论上分析了该拓扑的工作原理和电路的瞬时功率流向,从储能电容的不间断充放电过程中,计算出负载所需的无功功率.与传统的直流侧有源电力滤波相比,该拓扑具有调压范围广、储能电容充放电速度快、储能电容容值小的优点;且2个全控开关工作在同一...     

Multiple-critical-pole coupled active filters

In this paper realizations of low sensitivity narrow BP active filters implementing multiple-critical-pole (MCP) approximation methods and coupled filter structures are studied. In the first part of the paper, a synthesis procedure particularly developed for the realization of MCP transfer functions is described. According to that procedure the portion of the MCP transfer function containing multiple poles is realized as a follow-the-leader feedback (FLF) network, and the remaining part as a cascade. It is shown that the lower sensitivities of MCP functions in comparison with standard approximating functions (Butterworth, Chebyshev, etc.) can be further decreased by applying the FLF configuration instead of the cascade. the synthesis procedure is straightforward and in some cases it can be performed using identical second-order BP blocks. the final circuit sensitivities can be optimized according to given filter specifications and a user selected optimization criterion. In the second part of the paper, the MCP transfer functions are combined with the cascaded biquarts (CBQ), the shifted companion form (SCF), and the leap-frog (LF) structures, and sensitivity analysis is performed. It is shown that applications of the above mentioned structures can improve the filter sensitivites in a way similar to that of the given FLF configuration.     

Inverse active filters employing CFOAs

New configurations for realizing inverse lowpass, inverse bandpass, inverse highpass and inverse bandreject filters using commercially available current feedback op-amps (CFOA) with an accessible z-terminal such as AD844 are presented. The workability of the proposed circuits has been confirmed by experimental results employing AD844 type CFOAs.     

Generalized second-order active R filters

A generalized treatment of second-order active R filters is presented. A general circuit configuration is derived whose transfer functions are expressed in terms of defined resistive transfer functions and the gains of two operational amplifiers. The general network uses fewer resistances than reported configurations and can be used to realize all second order functions including oscillators. This approach facilitates simple and systematic analysis of second-order active R networks and leads to configurations having minimum component count.     

Application issues of active power filters

In this article, common nonlinear loads have been characterized into two types of harmonic sources, current-source type of harmonic source and voltage-source type of harmonic source. Compensation characteristics of both parallel active filters and series active filters have been discussed analytically and experimentally for these two types of harmonic sources. The corresponding required operation conditions, features, application issues, and adaptive harmonic sources of both filters have been presented. The fact that the traditional active filter, the parallel active filter, is not a panacea to harmonic compensation, and that one cannot use it blindly, has been clearly addressed. The parallel active filter will increase harmonic current and may cause overcurrent of the load when the load is a harmonic voltage source. Instead, it has been verified that the series active filter is better suited for compensation of a harmonic voltage source such as a diode rectifier with smoothing DC capacitor. The conclusions of this article also imply that when a parallel active filter is installed in a power system network such as at a point of common coupling, the network impedance and main harmonic sources downstream from the installation point should be investigated in order to get good performance and to minimize influence to the loads downstream. In some cases, a combined system of parallel active filter and series active filter may be necessary by utilizing the harmonic isolation function of the series active filters. No doubt active filters are superior to passive filters if used in their niche applications     

High-frequency limitations of rc-active filters containing simulated-l and fdnr elements

High quality RC-active filters may be realized using inductance-simulation or FDNR-synthesis techniques where generalized immittance converters (GIC) are the basic active two ports of the synthesis. The deterioration of the magnitude transfer function |T(jω)| at high frequencies is determined in terms of the gain bandwidth products B of the operational amplifiers employed within the GIC's. The basis of the method is to extend Blostein's lossless LC-twoport tolerance by determining the magnitude and phase errors of the simulated-inductance or FDNR elements.     

Compensation characteristics of shunt active and series active power filters

Active power filters have been used in practice to suppress the harmonic interference in power systems. To compensate for harmonic currents of loads, active power filters usually are connected to power systems in parallel with the loads. These filters, which are called shunt active filters here, are very effective for loads that can be considered as current sources, such as thyristor rectifiers with large dc reactances. Many papers have covered the shunt active filters applied to these current-source loads, however, none has discussed characteristics of the shunt active filters when they are applied to voltage-source loads. On the other hand, since more and more diode rectifiers with capacitive dc filters have recently been used, harmonics generated by them have become an issue. The diode rectifier with capacitive dc filters behaves as a voltage source rather than a current source. When a shunt active filter is applied to such a diode rectifier, the current injected from the shunt active filter may flow into the diode rectifier. As a result, harmonics of the source current cannot be reduced effectively, and harmonic current flowing into the diode rectifier increases greatly. This paper presents the aforementioned problem of shunt active filters analytically and experimentally. Then a series active filter is proposed to suppress the harmonic current of the diode rectifiers. The features, operating conditions, and considerations of shunt active filters and series active filters are described analytically and demonstrated experimentally. Taking a diode rectifier with capacitive dc filter as a typical voltage-source load, compensation characteristics of shunt active filters and series active filters are discussed by experiment and simulation. The validity of the series active filters is illustrated experimentally.     

Three-phase bipolar mode active power filters

In this paper, a unified constant-frequency integration control method for a three-phase bipolar mode active power filter is proposed. The proposed control method eliminates the use of any multipliers, the need of sensing three-phase load current, and the nontrivial task of calculating the harmonies and reactive current components, as required by previously reported control methods. By applying one-cycle control and sensing the mains line current, unity power factor and low input current distortion can be realized by one integrator with reset along with a few linear components such as flip-flops, comparators, and clock. The proposed controller is simple, robust, and reliable. All findings are supported by simulation and experiments     

RDFT算法在有源电力滤波器中的应用

提出了一种基于递归离散傅里叶变换(RDFT)的谐波检测算法,该算法采用滑窗迭代方法由离散傅里叶变换推导而来,具有运算量小、实时性好等特点,适合用数字信号处理器实现.并联型有源电力滤波器(APF)可以采用RDFT算法单独检测出非线性负载电流的基波成分与各次谐波成分,并根据需要生成补偿电流指令,实现对谐波电流的选择性补偿或...     

Design and performance of active power filters

This article has demonstrated the feasibility of a three phase active filter based on a half-bridge topology. Design guidelines for the power circuit have been derived and applied to a 5 kVA IGBT laboratory prototype. In the single phase mode, the active filter can reduce the low frequency harmonic content in the AC line to below 1% excluding the harmonics due to switching action of the converter. In the three phase mode, line currents are corrected under balanced and unbalanced conditions. The neutral current is reduced significantly.     

Multiloop feedback unsymmetrical active filters using quads

In this paper, a general design procedure for high order unsymmetrical active filters is presented using a special configuration of quads. Quads are 4th order subsection blocks using biquads in a special manner. It is shown that the determination of network parameters is not dependent on frequency range, and that the design procedure is simpler than other multiloop feedback (MF) topologies. The transmission zeros of the transfer function are derived directly from the zeros of the biquadratic blocks and thus feedforward or summation techniques are not required.     

Network conditioners on the basis of active filters

A novel control scheme for the stabilization of load voltage and the compensation for high harmonics of load current in series-type active power filter systems combined with shunt-type active power filters is proposed. The control system allows an effective correction of power factor, harmonic distortion, and load voltage regulation.     

基于遗传算法的有源滤波器优化设计

遗传算法(GA)是模拟生物在自然环境中的遗传和进化过程而形成的一种概率搜索算法,本文将遗传算法和全局优化的思想融合到一起来逼近切比雪夫有源低通滤波器.实验结果表明,这种方法克服了传统方法的一些不足之处,逼近效果有明显的改善.     

A simplified design-oriented analysis of switched-capacitor active filters

The method presented in this paper provides a simplified approach to obtain the z-domain equivalent circuit of an SC active filter by one-for-one substitution of each basic SC element with its z-domain equivalent admittance, if a specific terminal condition is met. Then, traditional circuit analysis techniques can be used to derive the z-domain transfer function of the filter. This method makes the analysis and the design of the SC active filter simple and similar to the S-domain method. Two application examples are given.     

串联型有源电力滤波器功率电路设计

主要讨论功率电路的设计方法，功率电路的设计主要和系统的稳态工作特性有关，因此首先对串联型有源电力滤波器进行了稳态分析，建立了系统的等效电路。然后。根据等效电路提出了一套基于稳态分析折功率电路设计方法，利用该方法推导出功率电路设计所要求的各个部分与电网电压畸变率，额定负载，负载功率因数及系统是否进行无功补偿的关系，得到了明确的解析表达式，所提方法和推导的结果均通过了实验验证。