Filter Design Method Research Articles

An Improved Resonant Frequency Based Systematic LCL Filter Design Method for Grid-Connected Inverter

Resonant frequency of an LCL filter in a grid-connected inverter is an important factor for control stability and grid-injected current quality. However, the constraints on resonant frequency are usually considered as an afterthought in conventional filter design methods. The fact that resonant frequency is affected by both internal and external factors during operation makes it even more critical. Hence, an improved resonant frequency based systematic LCL filter design method is presented in this paper. A resonant frequency band is identified by considering grid-voltage harmonics and control stability boundary. The variation in resonant frequency due to inductive line impedance as well as magnetic permeability of inductor core is taken into account to define the constraints on LCL parameters. The LCL parameters are then systematically derived from the identified constraints with almost no iteration. A division–summation (D-Σ) digital control method is used to validate the design method. Experimental results measured from a 5-kW single-phase grid-connected inverter have verified the effectiveness of the LCL filter design method over conventional methods.

Enhanced Sensor Monitoring to Maintain Optimal Aircraft Handling in Case of Faults

The design and validation of an advanced fault detection and diagnosis system to monitor the state-of-practice triplex redundant angle of attack measurement is presented. The proposed system fully solves the angle of attack sensor fault isolation problem. It thereby enhances the availability of the full control system functionalities in the case of multiple angle of attack sensor faults and helps to maintain optimal aircraft handling characteristics. The proposed fault detection and diagnosis system relies on advanced model-based and signal-based fault detection techniques. The used null-space-based method for the model-based fault detection filter design is extended to increase the filter robustness to model uncertainties. The developed approaches are applied and validated in realistic flight scenarios using a high-fidelity benchmark model of a large commercial transport aircraft. The reported results indicate that the use of the presented fault detection methods can help to maintain optimal aircraft handling in case of faults.

Delay-dependent stochastic finite-time ℓ1-gain filtering for discrete-time positive Markov jump linear systems with time-delay

This paper deals with the stochastic finite-time ℓ1-gain filtering problem for discrete-time positive Markov jump linear systems (MJLSs) with time-delay. By using twice augmentation system approach of the Markovianized system variables and further analyzing the relationship of finite-time boundedness and finite-time ℓ1-gain performance between the positive MJLS with time-delay and the augmented systems, a delay-dependent sufficient condition in the form of linear programming (LP) is established such that the resulting filtering error system is positive, stochastically finite-time bounded and has prescribed finite-time ℓ1-gain performance. Then the design of the stochastic finite-time positive ℓ1-gain filter is converted into solving some LP-based conditions. A numerical example is given to validate the proposed filtering design method.

H2/H∞ filtering for networked systems with data transmission time-varying delay, data packet dropout and sequence disorder

This paper investigates an H2/H∞ filter designing for networked systems perturbed by multiple noises. The measurement transmission from the sensor to the remote filter is completed via a communication network in simultaneously presenting of data transmission time-varying delays, data packet dropout and data sequence disorder. Since the filter will receive delayed and disordered information, a zero-order-hold (ZOH) or a logical-ZOH (LZOH) is firstly employed for resorting the chaos data sequence. Afterwards, a hybrid H2/H∞ filtering scheme is designed for accurately estimating the target output. By Itô formula and a novel free-weight method, the almost surely mean square exponentially stable (ASMSES) condition of the error system is conveniently obtained and the corresponding filter design method is finally presented. By the proposed method, not only the ASMSES with a pre-scheduled H2/H∞ performance can be achieved, but also the convergence rate of overall system is pre-regulable. In addition, it has been point out the dynamic filtering performance of LZOH scheme should be better than ZOH ones due to less time-varying delays are introduced and more latest measurement information are employed. Numerical examples are provided to demonstrate the effectiveness of the proposed methods.

A Fast Computer Aided Design Method for Filters

This paper presents a fast computer aided design method for filters based on model correction technique. Through the simulation of the submodels, the fitting formulas between the structure sizes and the coefficients can be determined. By pre-approved fitting formulas, the iterative correction is carried out on the filter structure sizes until the performance meets the specification. A design example is provided to explain the whole procedures. Simulation results agree well with the theoretical synthesis results which confirm the validity of the proposed method.

Reliable filtering with extended dissipativity for uncertain systems with discrete and distributed delays

ABSTRACTThis paper deals with the problem of reliable filter with extended dissipativity for uncertain systems with discrete and distributed delays, and sensor-failure model of this system is assumed to be concerned with Markovian behaviour. First, based on a novel Lyapunov–Krasovskii functional, a sufficient condition, which ensures that the filtering error system is stochastically stable and extended dissipative, is obtained. Second, mode-dependent conditions for the solvability to the reliable filter with extended dissipativity problem are given in terms of linear matrix inequalities (LMIs). The desired filter parameters can be derived by using feasible solutions to the presented LMIs. Finally, two numerical examples are given to illustrate the effectiveness of the filter design method.

Dissipative filter design for uncertain Markovian jump systems with mixed delays and unknown transition rates

In this paper, a partially mode-dependent dissipative filter design method is presented for uncertain Markovian jump systems with mixed delays and unknown transition rates. The uncertainty is assumed to be time-invariant which belongs to a ploytope. By constructing a mode-dependent and parameter-dependent Lyapunov–Krasovskii functional based on delay-partitioning approach, we propose a sufficient condition for the existence of a partially mode-dependent dissipative filter, which ensures that the resulting filtering error system is stochastically stable and dissipative. The filter parameters can be derived by using feasible solutions to a certain set of linear matrix inequalities. Finally, two simulation examples are provided to illustrate the effectiveness of the filter design technique.

New results on filter design for sampled‐data systems with packet dropouts and transmission delays

In this study, the problem of H ∞ filtering for sampled-data systems under unreliable communication links is investigated. The phenomena of data packet dropouts and signal transmission delays are addressed in a unified framework. The objective is to design an admissible filter to guarantee the asymptotic stability of the filtering error system and minimise the H ∞ disturbance attenuation level. Thanks to the proposed novel Lyapunov–Krasovskii functional together with the improved Wirtinger's inequality and the reciprocally convex approach, novel sufficient linear-matrix-inequality-based conditions are obtained for the existence and design of admissible filters. Finally, two simulation examples are provided to illustrate the efficiency and less conservativeness of the proposed H ∞ filter design methods.

A quad‐band bandpass filter using split‐ring based on T‐shaped stub‐loaded step‐impedance resonators

AbstractIn this article, a novel design method of multiband bandpass filters (BPFs) which have flexibly tunable center frequencies is presented by using T‐shaped stub‐loaded step‐impedance resonators (SLSIRs)’ multimode characteristics. By controlling the impedance ratios and the length ratios of the T‐shaped open stubs, the center frequencies of a multiband BPF can be decided. To verify the effectiveness of the proposed method, a 1.34/2.2/3.3/4.5 GHz quad‐band filter using split‐ring based on SLSIRs is designed, fabricated, and measured. The proposed filter is composed of a pair of tri‐section T‐shaped open stubs transmission lines, which form a folded split‐ring. By controlling the impedance ratios, the length ratios of the open stubs and the width of the gap of the folded split resonance loop, the quad‐band center frequencies are flexibly tunable. Owing to the 0° feed structure, seven transmission zeros can be realized near the pass‐band for enhancing the selectivity. The measured results show good agreement with the theory and the EM simulation.

Weighted‐average ℓ1 filtering for switched positive systems

SummaryIn this paper, the filtering problem for a class of switched positive systems with dwell time is investigated. A novel weighted‐average technique is proposed for filter design such that the final estimate of the unmeasurable outputs of the considered system is more accurate than that of traditional approaches. The main contributions of this paper are summarized as follows: By exploiting the positivity and characteristics of switched positive systems with dwell time, a candidate linear copositive Lyapunov function, which is both quasi‐time‐dependent and mode‐dependent, is presented to establish the closed‐loop stability of the considered systems. Upon the established closed‐loop stability, less conservative bounded positive filters (both upper‐bound and lower‐bound filter) with ℓ1 disturbance attenuation performance are designed for the considered system. By introducing a proper weight, a weighted‐average approach, which is more general than the bounded filter design method, is proposed for filter design. The worst ℓ1 disturbance attenuation performance of the novel developed filter is evaluated. Both the bounded filters and the weighted‐average filter are designed by solving standard linear programming problems. A numerical example illustrates the effectiveness of the proposed approach. Copyright © 2017 John Wiley & Sons, Ltd.

A designing method for band‐reject filter with high selectivity and tunable bandwidth

AbstractHigh selectivity band‐reject filters are usually demanded in applications such as removing QAM signals of digital cable TV network and removing interference signals in communication systems. In this letter, a filter design method which employ discontinuous meandered transmission line and isolated board is proposed. The experimental results show that the transient bandwidth (between −3 and −20 dB) of our filters is less than 1 MHz. Besides, the rejecting bandwidth of our filters can be tuned to fulfill the requirements of different applications.

Implementation of fractional order filters discretized by modified Fractional Order Darwinian Particle Swarm Optimization

Digital systems are placed at the core of information technology and they are used extensively in electronics. The digital filter realization has become a central topic of signal processing studies. This paper presents a discrete IIR filter design method for approximate realization of fractional order continuous filters in digital systems. For this purpose, Fractional Order Darwinian Particle Swarm Optimization (FODPSO) method is modified to provide better fitting of a discrete IIR filter function to a fractional order continuous filter and we implemented a hybrid version of FODPSO method, where the initial particle generation is carried out by arithmetical candidate point selection technique of the Base Optimization Algorithm (BaOA). This modification expands the search range of the FODPSO and thus the optimized discrete IIR filter can provide better approximation to amplitude response of fractional order continuous filter functions. In the paper, several illustrative examples are presented to demonstrate the performance of proposed methods.

Event-triggered fault detection for discrete-time Lipschitz nonlinear networked systems in finite-frequency domain

The problem of event-triggered fault detection (FD) filter design for discrete-time Lipschitz nonlinear networked systems with finite-frequency specifications is investigated. The event-triggered transmission scheme is introduced to mitigate the utility of limited network bandwidth. The developed filter combines the H∞ and H− indices. For this class of systems, the generalized Kalman–Yakubovic–Popov lemma-based finite-frequency FD filter design methods are invalid. To solve this problem, the nonlinear error dynamics are transformed into a linear parameter varying (LPV) system based on the use of a reformulated Lipschitz property and a new lemma is developed to capture the system performances in finite-frequency domain. By introducing slack variable techniques, sufficient conditions for the design of FD filter are derived in terms of linear matrix inequalities (LMIs). The proposed design method can significantly reduce the data transmission and achieve a better FD performance than that in full frequency domain. Finally, two examples are presented to validate the effectiveness and superiority of the new results.

Networked filtering for Markovian jump T–S fuzzy systems with imperfect premise matching

This study focuses on networked H ∞ fuzzy filtering for Markovian jump Takagi-Sugeno (T-S) fuzzy systems. Since the traditional PDC method is ineffective under network environments, a flexible filter design method is provided with imperfect premise matching. First, a unified T-S fuzzy error model is provided by considering the mismatched grades of membership. Second, by use of the constructed model and the Markovian switched Lyapunov-Krasovskii functional, a stability and a stabilisation criteria of the fuzzy filtering error system are derived, in which it is no required that the fuzzy filter shares the same membership functions with the fuzzy systems. Therefore, the designed filter is available under network environments since the mismatched premises induced by networks are well considered. Finally, the effectiveness of the proposed new design method is illustrated by two examples.

Novel programmable microwave photonic filter with arbitrary filtering shape and linear phase.

We propose and demonstrate a novel optical frequency comb (OFC) based microwave photonic filter which is able to realize arbitrary filtering shape with linear phase response. The shape of filter response is software programmable using finite impulse response (FIR) filter design method. By shaping the OFC spectrum using a programmable waveshaper, we can realize designed amplitude of FIR taps. Positive and negative sign of FIR taps are achieved by balanced photo-detection. The double sideband (DSB) modulation and symmetric distribution of filter taps are used to maintain the linear phase condition. In the experiment, we realize a fully programmable filter in the range from DC to 13.88 GHz. Four basic types of filters (lowpass, highpass, bandpass and bandstop) with different bandwidths, cut-off frequencies and central frequencies are generated. Also a triple-passband filter is realized in our experiment. To the best of our knowledge, it is the first demonstration of a programmable multiple passband MPF with linear phase response. The experiment shows good agreement with the theoretical result.

An improved H ∞ fuzzy filter for nonlinear sampled-data systems

This paper presents an H ∞ fuzzy filter design method for nonlinear sampled-data systems that are represented by a Takagi–Sugeno (T–S) fuzzy model. An error system between the T–S fuzzy system and the fuzzy filter is obtained to analyze the sampled-data system and solve the filter synthesis problem. To enhance the feasibility of the sampled-data fuzzy filter, an improved approach is proposed that not only captures the characteristics of the sampled-data system, but also eliminates a complex discretized model of the sampled-data system using a Lyapunov function and two null terms. In the sense of Lyapunov, relaxed sufficient conditions, which are derived in terms of linear matrix inequalities (LMIs), are obtained for both asymptotic stability and H ∞ disturbance attenuation performance of the error system with less conservatism. Finally, simulation examples are presented to show the effectiveness of the proposed method.

Fuzzy filter for nonlinear sampled-data systems: Intelligent digital redesign approach

This paper presents a fuzzy filter design method for nonlinear sampled-data systems using an intelligent digital redesign (IDR) technique. Based on a Takagi–Sugeno (T–S) fuzzy model, discretized closed-loop systems with pre-designed analog fuzzy and digital fuzzy filters are presented. An IDR problem is given to guarantee both state-matching condition and asymptotic stability. Sufficient conditions for solving the IDR problem are proposed and are derived in terms of linear matrix inequalities (LMIs). Finally, a simulation example is given to show the effectiveness of the proposed method.

A New Synthesis and Design Method for Wideband Bandpass Filters With Generalized Unit Elements

A new synthesis and design method for wideband bandpass filters has been proposed using the concept of generalized unit elements (GUEs). The synthesis starts with a lumped-element LC circuit, which is obtained by some well-known circuits and classic methods, such as the ladder-type circuit and the coupling matrix method. A GUE is an equivalent circuit, which is represented by either a coupled LC circuit or a section of the transmission line coupled by stubs. In this view, an LC circuit is transformed into the transmission line circuit directly via a general network of a GUE. This contributes to the key idea behind the synthesis procedure. Detailed analysis on the GUE and its equivalent circuits are discussed in terms of the equivalent characteristic impedance and the extended Richard’s transformation. Based on these two variables, frequency and constant mapping functions are proposed to explicitly obtain characteristic impedances in the transmission line circuit. In the final part, three prototype filters, namely, the classic Chebyshev ladder-type filter, the general box-shaped Chebyshev filter of symmetrical filtering responses, and the cascaded trisection filter in an asymmetrical transmission zero distribution are designed and fabricated, respectively. All the experimental results agree well with the predicted ones and thus it verifies the proposed synthesis and design method.

Design of a CLC Filter for Flyback-Type Micro-inverters of Grid-Connected Photovoltaic Systems

ABSTRACT In this paper, the design method of CLC filter for current source inverter (CSI) is discussed. This inverter is basically for photovoltaic system with small power which is also called micro-inverter. For better performance of small power inverter, flyback-type converter-side topology is determined and it operates as CSI because it has inductor inside. The CLC filter is the output filter for this CSI. Mostly, the components’ capacity and system size are regarded as key factors when evaluating small-powered systems. The CLC filter is made with an additional capacitor to a conventional CL filter. The proposed CLC filter assures the same or the better performance on current ripple reduction than the CL filter. Hence, according to this output filter benefits, the micro-inverter system can be smaller and cost down. The passive damping methods are also analysed upon the positions of resistive damping in the filter circuit. Among four different damping methods according to the resisters’ position, the optimal damping method which has the lowest power consumption is applied to the proposed CLC filter and the effect of this method is also analysed. Performance of the proposed CLC filter is verified with simulation and experiment and the results also show the validity of passive damping method.

A novel evolutionary method of structure-diversified digital filter design and its experimental study

Digital filters are now key components in many modern digital systems. This paper proposed a novel evolutionary method to design structure-diversified digital filters. On the investigation of the existing evolution-based digital filter design methods, most state-of-the-art works concentrate on the evolution of appropriate transfer functions for digital filters. However, a transfer function is not equivalent to a practical digital filter that has proper structure and can be implemented by a hardware directly. Some researchers proposed a synthesis method to generate the structure of digital filter from a specified transfer function. However, this method needs an existing transfer function as the prior knowledge. Compared with existing works on the evolution of digital filters, the proposed method is novel at the following aspect: the proposed method can directly evolve the structure and parameters of digital filter without the pre-definition of the transfer function. The only prior knowledge we need is the specification of the design target, such as the frequency range of the passband and stop-band. In the experimental study, a significant characteristic is revealed that the proposed method is able to evolve structure-diversified filters with approximate frequency response. The proposed method is a prototype, and it is demonstrated to be a promising way of digital filter design.