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This paper proposes a new type of hybrid eighth‐mode substrate integrated waveguide (EMSIW) and microstrip line (MSL) bandpass filter (BPF) with mixed electric and magnetic coupling. Firstly, two second‐order EMSIW BPFs with mixed coupling and wide stopband performance are investigated. Then, in order to realise high‐order BPF with decent performance, half‐wavelength (λ/2) open‐circuited MSL resonators are employed in the hybrid BPFs design. In the end, two third‐order BPFs and a fourth‐order BPF are developed by combining the EMSIW and MSL resonators together. Extra transmission zeros can be introduced due to the cross couplings in the trisection and quadruplet topologies. For demonstration, the proposed prototypes are designed, fabricated and measured. Reasonable agreements can be achieved between the measurement and simulation. The proposed third‐order BPFs compete against the state of the art, exhibiting the competitive characteristics of the operating bandwidth, physical footprint and upper‐stopband rejection with less order. The proposed fourth‐order BPF features a compact size of 0.34 × 0.34λ0, a low insertion loss of 1 dB, a broad 3‐dB fractional bandwidth of 22.9% and an excellent lower‐stopband suppression. [ABSTRACT FROM AUTHOR]

With the development of photovoltaic power generation technology, a large number of micro-power grid with distributed generation system have appeared in remote areas. It has the longer transmission line between the traditional power grid and the inverter of the distributed generation system. This caused the equivalent network impedance would be increased and would weak the power-grid characteristics. When the photovoltaic inverter is connected to a weaker power grid, the bandwidth of the control system of the inverter will be reduced. Using the traditional PR control to solve the problem is not ideal. This paper proposes fuzzy quasi-PRD control to improve the current quality. The inverter with the LCL filter has the peak of the resonance oscillation, it will affect the stability of the system. The paper adopts the adjustable virtual damping to suppress resonance. At last, the idea is verified by MATLAB/Simulink. The results show that the fuzzy quasi-PRD control method has better control performance, and dynamic tracking characteristics. [ABSTRACT FROM AUTHOR]

The converter is the main component of the converter station and the main noise source of the PLC interference. The accurate modelling of the high-frequency characteristics of the converter is the foundation for the design of the ± 1100 kV UHVDC PLC filter. Based on deep analysis of the high-frequency characteristics of the converter valve, this paper first proposes three high-frequency models of the converter valve. Compared with a real converter valve used in similar HVDC project, model two is chosen to analyse the high-frequency characteristics. Second, the model of Zhundong–Wannan UHVDC transmission project is established in the PSCAD simulation platform to determine the actual high-frequency characteristics of the converter valve. The voltage before the smoothing reactor is calculated, and the high-frequency noise level is obtained by Fourier transform. Considering the practical application of the high-frequency model of the converter valve, this paper finally proposes a formula to express the measured noise level. The noise source expressed by the formula is more practical for research on high-frequency characteristics of the converter station. [ABSTRACT FROM AUTHOR]

This paper proposes three balanced multiple‐layer dual‐mode substrate integrated waveguide (SIW) bandpass filters. The first balanced filter has two substrate layers, and two pairs of balanced feeding ports are located on the upper substrate layer. The lower and upper dual‐mode SIW cavities are coupled by two crossed slots in the middle metal layer. The second balanced filter has two substrate layers, and two pairs of balanced feeding ports locate parallelly on the upper and lower substrate layers, respectively. The third balanced filter has three substrate layers, and two pairs of balanced feeding ports locate vertically on the upper and lower substrate layers, respectively. The proposed three balanced filters can produce three, two and one finite‐transmission zeros (FTZs), respectively. Characteristics of the proposed multiple‐layer SIW filters with controllable FTZs' locations are analysed in detail. For the demonstration, some design examples with the centre frequency of 7.5 GHz and bandwidth of 240 MHz are presented, and three design examples are fabricated to verify the performance of the proposed balanced filters. The measured results agree well with simulated ones. [ABSTRACT FROM AUTHOR]

Cross‐coupled microwave filter with flexible topology is an essential component in a modern communication system. Among the various filter networks, the use of an extended box section can effectively reduce the difficulty of filter design, but the synthesis approach for this popular structure is not well developed. This paper presents the synthesis method based on the folded coupling matrix to derive the extended box sections. At the same time, an eighth‐degree filter with extended sixth‐degree box sections is synthesized to demonstrate the correctness of the approach. Finally, the new approach's feature to derive advanced circuits such as peculiar quintets is discussed, indicating that it has certain universality. [ABSTRACT FROM AUTHOR]

This paper proposes a new time‐resolved spectral analysis method based on a modification to the linear predictive coding (LPC) method for enhancing the identification of the dominant frequencies of a signal. The method described here is based on a z‐plane analysis of the LPC poles. These poles are used to produce a series of reduced order filter transfer functions which can accurately identify and estimate the frequency of the dominant spectral features. The standard LPC method has been shown to suffer from a sensitivity to noise and its performance is dependent on the filter order. The proposed method can accurately identify the dominant frequency components over a range of filter orders and is shown to be robust in the presence of noise. Compared with traditional time‐resolved methods, it is a parameterised method where the identification of the dominant frequency changes can be directly obtained in the form of frequency measurements. In a series of 10,000 Monte Carlo experiments on single component and multiple component signals, this LPC pole processing method outperforms the standard LPC method by accurately identifying the dominant frequency components in the signals. [ABSTRACT FROM AUTHOR]

This paper presents a tri‐wideband bandpass filter (TWB‐BPF) with compact size, high band‐to‐band isolation, and multiple transmission zeros (TZs). The proposed TWB‐BPF is based on a multiple‐mode resonator (MMR), which is interpreted by the method of the even‐ and odd‐mode analysis technique. The MMR can excite 11 resonant modes, where the first two modes comprise the first passband, the next four modes form the second passband, and the last five modes are used to generate the third passband. In addition, 10 TZs are yielded to obtain high band‐to‐band isolation and wide stopband suppression characteristics up to 14.95fc1 (fc1 is the center frequency of the first passband). To verify the proposed filter, a TWB‐BPF with 3‐dB fractional bandwidths (FBWs) of 37.4%, 43.5%, and 40.4% is designed, fabricated, and measured. [ABSTRACT FROM AUTHOR]

Filters are inevitable for grid‐connected inverters to attenuate the current harmonics caused by the pulse width modulation which is usually used in power conversion systems. High‐order filters have attracted much attention because they attenuate the current harmonics effectively. Nevertheless, the high‐order filters have some resonances which cause instability of the system. In addition, the resonance frequencies shift to high as the inductors and capacitors are smaller. It implies that the resonance frequencies may be beyond the Nyquist frequency in downsizing the filter. This complicates the stability and performance analyses of the system. This paper investigates rigorous input–output stability and analyses a robust performance based on the sampled‐data control theory regardless of whether the resonance frequencies are beyond the Nyquist frequency or not. Our analysis contributes to downsizing the filter synthesis while the stability and the robustness are guaranteed even if the resonance frequencies are beyond the Nyquist frequency. The effectiveness of the proposed method is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

Recently, there have been many visual tracking methods based on correlation filters. These methods mainly enhance the tracking performances by considering the information of background, space, or time in the appearance model. This paper proposes an effective tracking method, named adaptive spatial–temporal regularized correlation filter (ASTRCF) tracker, based on the popular adaptive spatially regularized correlation filter (ASRCF) tracker. That is, the continuity of object's motion in the process of tracking is considered by introducing a temporal‐regularized term in the appearance model of ASRCF tracker. Furthermore, its solution is inferred by applying the alternating direction method of multipliers. The proposed appearance model contains a background‐awareness term, a spatially regularized term, an adaptive‐weight term, and a temporal‐regularized term. Therefore, it can not only keep the good performances of ASRCF tracker, such as learning the background information and the spatial information adaptively to enhance the discriminating ability, but also take advantage of the relation of correlation filters in the last frame and the current frame for addressing the complex cases, such as occlusion, and fast motion. Extensive experimental results on various challenging databases show that the proposed ASTRCF tracker achieves better tracking performances than some state‐of‐the‐art trackers. [ABSTRACT FROM AUTHOR]

With the development of global navigation satellite system (GNSS), the GNSS/inertial navigation system (INS) integrated system offers the users better positioning or navigation performance. This paper proposes an adaptive robust ultratightly coupled GNSS/INS system based on a novel vector tracking strategy for combining both global positioning system (GPS) L1 and BeiDou B1 signals' tracking together. The inherent mechanism of the vector tracking approach has been analysed to describe the relationship between the replica signals and user's dynamic state. Then, an adaptive robust filter is used to gain the accurate estimates of vehicle states when the vehicle is under a weak-signal or large manoeuvring environment. Finally, the experimental platform is set up using a GPS/BeiDou signal simulator and an inertial measurement unit simulator and the test results show that the proposed ultra-tightly coupled system can keep the tracking loops from the high dynamic perturbations, which saves the cost time of signal reacquisition. Moreover, the presented adaptive robust ultratightly coupled system can obtain a higher accuracy than Kalman filtering in a simultaneous weak-signal and large manoeuvring environment. [ABSTRACT FROM AUTHOR]

Here, a novel design of absorber loading dual‐layer frequency selective surfaces (FSSs) in the Salisbury screen is proposed. The design of frequency selective surfaces is mainly composed of cross‐dipole and dual‐loop metal patch. Simulation results show that this absorbing structure can achieve ultra‐wideband absorption from C band to K band and the fractional bandwidth reaches 117.1% below –10 dB. The thickness of the proposed absorbing structure is 0.078 λL and the unit cell size is 0.262 λL, where λL is the wavelength of the lowest absorbing frequency. Moreover, it shows excellent polarization stability in TE and TM modes, and it has great angular stability. Finally, the prototype of this structure is fabricated, and the measured results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

This study proposes an iterative design method of L-type Inductor, Capacitor, and L-type Inductor (LCL) filter for grid-connected converter to achieve optimal filter parameter combination. LCL filter is commonly used for to reduce high frequency harmonic pollutions being injected into distributed power network. Accordingly, the performance of harmonics attenuation is taken as the most decisive constraint for filter parameter design. Usually, traditional methods apply the full-modulated operating condition to acquire amplitudes of present voltage harmonics, leading to over-designed capability of harmonics attenuation, which means increased inductance, degraded dynamic response, and enlarged weight and space. To deal with these challenges, the harmonic distortion factor is first proposed to evaluate the influence of different order voltage harmonic on grid current distortion. Also then, with four deduced constraint functions, an iterative design procedure is proposed to obtain satisfactory region of all filter parameters. As a result, the capability of harmonics attenuation can be precisely designed, and the optimal parameter combination brings about significant reduction of filter inductance. For instance, compared with the traditional method, the total inductance can be reduced by 23.3% in a 10 kW system. Finally, the experimental results are presented to demonstrate the effectiveness of proposed method. [ABSTRACT FROM AUTHOR]

A simple double-layer grid plane wave filter structure is proposed that can provide multiple transmission bands for cellular phone frequencies but with a reflection band for wireless local area network signals. The approach offers ease of construction making it applicable to building applications. A parametric study using simulation supported by simple experimental data investigates the proposed, novel design. [ABSTRACT FROM AUTHOR]

This study presents a 60 GHz quasi-elliptic bandpass filter with a compact and planar structure. The proposed filter was constructed by stacking substrate integrated waveguide (SIW) cavities on the central transverse plane of a shielding SIW cavity. Jerusalem cross (JC) apertures and circular apertures were etched on the metal layers of the stacked SIW cavities to enable dual-mode operation and energy coupling. In the dual-mode cavities, the TM110 cavity mode and JC aperture mode can be excited simultaneously. Cross-mutual couplings exist among the resonant modes, resulting in two finite transmission zeros with each at either side of the passband. Multilayer low-temperature cofired ceramic technology was adopted to manufacture the experimental filter. The measured centre frequency was 60 GHz at a fractional bandwidth of 4.5% with two finite transmission zeros located at 53.7 and 65 GHz, thereby achieving highfrequency selectivity. [ABSTRACT FROM AUTHOR]

A balanced quad-band diplexer is proposed with wide common-mode (CM) suppression and high differentialmode (DM) isolation in this study. The six-port balanced diplexer was formed by combining two dual-band bandpass filters operating at 1.92/5.25 and 2.45/5.8 GHz through two stepped-impedance resonator (SIR) inserted T-junctions. By carefully designing the section length of the T-junction and the SIR length from its open-end to the joint-point with the T-junction, high isolation between diplexer channels can be attained. A prototype of the proposed balanced quad-band diplexer was implemented and measured with a DM isolation of higher than 51.8 dB and a CM suppression of larger than 47.9 dB in the four DM passbands. Good agreement was observed between the simulated and the measured results. [ABSTRACT FROM AUTHOR]

As the grid-connected converter is operating in the unbalanced three-phase grid in the traditional control strategies, the even harmonics of the voltage appear in DC-link and the odd harmonics of the current in AC-link, which will severely affect the performance of the grid-connected converter. Under this circumstance, the unbalanced threephase grid will bring various negative effects and difficulty to the control of the converter, such as the fluctuation of active and reactive powers, non-sinusoidal and unsymmetrical three-phase currents. First, this study analyses the form of the fluctuation of power based on the instantaneous power theory and establishes a mathematical model of a gridconnected converter under unbalanced grid voltage. And then, a more complete description of the control problem of the converter is given, after three different control objectives, the fluctuation of active/reactive power and the nonsinusoidal and unsymmetrical grid currents, are considered at the same time. A novel method of separating the instantaneous positive and negative sequence components is proposed and well applied during achieving the different control objectives. Finally, the experimental results are compared, showing that the strategy is effective. [ABSTRACT FROM AUTHOR]

Design procedure of a novel transmission line low‐pass filter is presented. The filter has a flexible rejection response for a prescribed cut‐off frequency and an in‐band ripple factor. It is compact by using a Z‐shaped coupled‐line section, which is loaded with open‐circuited stubs. All of the transmission line elements are identical in electrical length, and the impedances can be calculated by solving certain specific equations according to prescribed in‐band specifications. The simulated results show that the circuit can generate low‐pass responses with third‐, fifth‐, and seventh‐order filtering functions. The filter order depends on the number and position of the loading stubs. For verification, two sample filters with cut‐off frequency of 0.5/0.3 GHz are fabricated using a three‐/five‐layer PCB process, which generate seventh‐order low‐pass filtering responses with good selectivity. The experimental results agree well with the predictions. [ABSTRACT FROM AUTHOR]

A new bandpass filter (BPF) with two switchable operating passbands has been proposed. The BPF topology is formed by switchable resonators and stepped‐impedance resonators. The two operating bands can be switched on and off independently. For verification, a switchable BPF with a third‐order Chebyshev bandpass response was designed and fabricated using microstrip technology. The developed BPF was measured to verify the predicted and simulated results. A close agreement was observed between them. The proposed switchable BPF has good in‐band and out‐of‐band performances. Besides, the attenuation is > 30 dB as the passband is switched off. [ABSTRACT FROM AUTHOR]

A design method of compact wideband balun bandpass filter (BPF) with high selectivity based on corrugated slot is proposed here. To realize wideband balun response in compact size, metal strips are deployed parallel to the half‐mode corrugated slot (HMCS). Besides, the coupling of corrugated slot to the metal stripline provides the conversion of slot to microstrip structure at the balanced ports. By placing a pair of resonators at the balanced ports, a wideband balun BPF response with high selectivity can be realized. In addition, a U‐shaped resonator is also loaded at the end of the corrugated slot to suppress harmonics. Afterwards, a compact wideband balun BPF centred at 2.42 GHz with 3‐dB FBW of 45% is designed, fabricated, and measured. The effective size is 0.13λg × 0.39λg (λg is the guided wavelength of the centre frequency) and the measured results indicate that the magnitude imbalance is less than 0.45 dB and the phase imbalance is less than 4.8° within the operation frequency band. [ABSTRACT FROM AUTHOR]

To reject the disturbances of the nonminimum‐phase systems, the generalised dual‐filter disturbance observer is proposed. The conventional disturbance observer methods inevitably lead to nonminimum‐phase systems' instability. To stabilise the system, the forward plant and dual filters are introduced. The stability constraints are transferred to the dual filters. Based on any stable designs of the close‐loop controller, the dual filters can be easily designed. The simulations effectively verify that the disturbance rejection performances of the proposed method are triple those of the closed‐loop nonminimum‐phase system, and the original system's tracking capabilities and stability margins are few affected. [ABSTRACT FROM AUTHOR]

An equivalent circuit model of double hexagonal loops frequency selective surface (FSS) was established. The formulas of LC parameters were proposed with equivalent repetition period. The reflection frequency, transmission frequency, and the location of first modal interaction null were simulated, and the results showed a good agreement in full-wave simulation result. On this basis, an ultra-wideband composite absorbing material (CAM) was proposed, and its equivalent circuit model was also established. A sample was fabricated and measured to verify the validity of the model. The results showed a good ultra-wideband absorbing performance in the range of 1.9–8.9 GHz. [ABSTRACT FROM AUTHOR]

The letter presents a triple‐mode short‐circuited circular patch resonator for bandpass filter (BPF) design. The resonator employs the TM010 mode as its dominant mode, the resonant frequency of which is lower than that of the TM110 mode. In addition, four radial slots are etched on the patch to extend the current paths of the TM110 and TM210 modes, shifting down the resonant frequencies of the two modes. The adjacent triple modes can be used to design wideband BPF. Meanwhile, the centre frequency (CF) and bandwidth (BW) can be tuned by the length of the slots. Furthermore, the short‐circuited vias are arranged in a circle providing a tuneable parameter to control the CF and BW as well. According to the symmetry of the geometry, the resonator can be bisected to realise half‐mode resonance. Two cascaded half‐mode semi‐circular patch resonators are applied to design BPF with high selectivity. BPFs using the circular patch resonator and the semi‐circular patch resonator are designed and measured for demonstration. [ABSTRACT FROM AUTHOR]

This letter reports an accurate and rigorous design method for a distributed‐element reflectionless bandpass filter capable of producing a reflectionless response at two ports simultaneously. The design method relies on novel transmission‐line reflectionless filter prototypes. This work presents a stub‐based reflectionless filter prototype and its design formulas in terms of a target transmission response. It also provides a stub‐less coupled‐line reflectionless filter prototype equivalent to the stub‐based prototype in case where stubs are not feasible. A second‐order bandpass filter has been designed and fabricated to verify the design method. Reasonable agreement between the measured performance and the simulated one has been obtained, confirming that the proposed design is valid. [ABSTRACT FROM AUTHOR]

Switching AC filter may cause harmonic impact, which may lead to commutation failure of HVDC system. Here, the commutation failure mechanism of HVDC system caused by AC filter switching is studied. The circuit and mathematical model of the transient process simulation of filter switching are established, and the time-domain solution of the overvoltage of each filter including voltage reduction and distortion is given. The commutation failure mechanism of HVDC system is analysed based on the commutation failure analysis method of harmonic voltage and time area. The simulation results verify the effectiveness of the mechanism analysis of commutation failure caused by AC filter switching in HVDC system. [ABSTRACT FROM AUTHOR]

AC filter is an important part of HVDC system, which can restrain the AC-side harmonics effectively and compensate for the reactive power consumed by converter station. Due to the harmonic characters of converter, double-tuned filter and triple-tuned filter are widely used in HVDC system. There is no model of double-tuned filter or triple-tuned filter in the common simulation software such as ETAP and DIgSILENT, which brought some difficulties to the simulation of HVDC especially harmonic analysis. To solve this problem, the accurate and simplified calculation method for equivalent models which instead double-tuned filter and triple-tuned filter by two parallel single-tuned filters or three parallel single-tuned filters are proposed. Furthermore, the accurate formulas and simplified formulas are given which can convert the parameters of double-tuned filter or triple-tuned filter to the parameters of parallel single-tuned filters. Taking into account of the complexity of the accurate formulas, the resonant frequencies of double-tuned filter and triple-tuned filter are considered in the simplified formulas, which simplified the computational complexity. Finally, the feasibility of the equating method and the validity of parameters calculation method are verified. [ABSTRACT FROM AUTHOR]

In hierarchically connected UHV DC projects, the 1000 kV AC filter sub-bank in converter station is provided with two 500 kV circuit breakers. To determine the test DC component decay time constant when breakers break short-circuit current, relevant DC project was modelled in electromagnetic transient program (EMTP) for calculations. It is pointed out that for UHV AC filter circuit breakers, the decay time constant of DC component of short-circuit current should be determined solely based on the single-phase to earth fault current. Calculations and analyses were made of the AC and DC components and the DC component decay time constant of filter single-phase to earth fault current, and the time constant calculated was converted to the test value of breakers with rated short-circuit breaking current of 63 kA. According to the research results, a time constant of 75 or 90 ms is recommended for the two 500 kV circuit breakers, and it is lower than 120 ms as required by the relevant standards, providing technical support for future breaker tests. [ABSTRACT FROM AUTHOR]

The internal model controller-proportional-integral-derivative (IMC-PID) is one of the simplest model based proportional-integral-derivative (PID) design methods available in the literature. In IMC-PID design, the three variable PID design problem is converted into the single variable design problem with the help of the internal model of the process and an internal model controller (IMC) filter. The IMC filter is used to control the robustness of the process and transient performance. The IMC filter, however, introduces additional phase lag in the process, due to which the stability of the process is compromised to maintain the transient response. In this study, a new indirect design approach of IMC-PID controller is proposed for first-order filter with dead time (FOPDT) and second-order filter with dead time (SOPDT) processes, in which the IMC-PID controller is designed for the pole-zero shifted process instead of original process and the process robustness is tuned with the help of the proposed shifting constant ψ. The proposed design does not involve any IMC filter, which helps to achieve a better IAE and higher Phase Margin at desired Maximum Sensitivity. The proposed method is validated with the help of real-time experiment on water level control of Canonical Tank System and MATLAB simulation examples of the FOPDT and SOPDT processes. [ABSTRACT FROM AUTHOR]

The conversion and utilisation of renewable energy generations often require grid-connected inverters. When applying LCL filter to remove power electronic chopping harmonics, the power quality faces two issues of resonance damping and grid voltage induced current distortion. Conventionally, two separate control algorithms are required to treat the two issues, requiring an additional current sensor, increasing control complexity and limiting performance. This study demonstrates that linear active disturbance rejection control (ADRC) is able to treat both resonance damping and grid voltage induced current distortion as overall disturbance at the same time through a single structure, while achieving higher power quality for dynamic, steady-state, small and large parameter setup, as well as parameter variations, as validated by experimental results. In principle, the ADRC can be configured with or without knowledge of the system model. This study also reveals that it is the measurement noise tolerance that makes the two configurations different in practice. By using model information in ADRC algorithm, the required bandwidth can be reduced, offering more tolerance to measurement noise. Moreover, the ADRC controller has only two parameters to tune for 'fast' or 'slow', which makes it easy for implementation. [ABSTRACT FROM AUTHOR]

A new design technique of a dual-mode ring-resonator suspended-substrate stripline filter is reported here to achieve low passband insertion loss, high quality factor, and good spurious response. A fourth-order bandpass filter was designed and fabricated at the operational frequency of 2.07 GHz with two ring resonators packaged in a metallic cavity where each ring resonator is one wavelength long. The transmission zeros of the dual-mode filter are generated due to the phase cancellation between the two paths in a ring, thus a sharp-skirt selectivity filter response was achieved. Perturbation notch structure was implemented on each ring resonator to provide the electromagnetic coupling of two degenerate modes, thus a dual-mode response of the filter can be synthesised. Measurement results of the first dual-mode filter prototype showed a return loss and an insertion loss of better than 16.42 and 0.926 dB, respectively, while an out-of-band rejection of up to 55 dB was achieved. The novel filter design technique proved that no cross-coupling is required to obtain the transmission zeros of the filter, thus the sharp-skirt response was achievable. [ABSTRACT FROM AUTHOR]

An LCL-filter draws much attention in grid-connected applications, but the design faces challenges. The LCL and controller parameters are interdependent and inter-restricted as the grid current quality and control stability rely on the parameters of them both. In the past, researchers found that extra sensors or complex algorithms were required for the stability when the LCL parameters were designed independently. Consequently, the system cost and complexity were increased. Indeed, the LCL-filter with the delay-dependent single-loop current control can be stable if the LCL parameters are properly selected. Based on this thought, this study proposes to design the LCL parameters by considering their impact on the stability and dynamic of the inverter. Extra sensors or complex algorithms are no longer required. Based on establishing the model of the single-loop inverter-side current controlled inverter, the criteria of LCL design are obtained in order to improve the stability and the rejections of low-order and switching current harmonics. Based on those design criteria, a step-by-step procedure is proposed. Selected results have been provided to demonstrate the effectiveness of the proposed design. [ABSTRACT FROM AUTHOR]

A correction to the article "Design of Absorptive Superconducting Filter" in the 2017 issue is presented.

This study is concerned with the development of millimetre wave substrate integrated waveguide (SIW) diplexers, with an aim of relaxing fabrication tolerances. A method of designing SIW components initially in a dielectric filled waveguide (DWG) medium, and then translating a final optimised design to SIW is presented. Owing to the equivalence between SIW and DWG, the translated SIW components do not require a further optimisation which is a significant advantage as it speeds up the design process. The authors demonstrate this process by presenting the design of a Ka-band diplexer that consists of a highpass filter, hybrid coupler and low-order bandpass filter, where good agreement between the DWG and translated SIW cases can be observed. To investigate how the diplexer handles fabrication errors, the authors subjected the circuit to a tolerance analysis where simulated results suggest that the highpass filter in the diplexer is less sensitive to fabrication errors than the bandpass filter and its use in millimetre wave SIW diplexer circuits can help to relax sensitivity to fabrication errors. These observations are verified with the measurement of a fabricated Ka-band SIW diplexer, where the measured and simulated S-parameters are in very good agreement. [ABSTRACT FROM AUTHOR]

Ground leakage current in a power converter is a major concern, which has stringent limitations due to safety concerns. Presence of high-frequency pulses, with high dv/dt due to switching actions in common-mode (CM) voltage, result in injection of current waveforms with large di/dt spikes into the ground and causes high electromagnetic interference (EMI) noise level. In this study, a new method is proposed to make the CM voltage, of a single-phase grid-connected inverter, sinusoidal and free of high-frequency pulses. The proposed method consists of two parallel connected H-bridge power converters, which uses unipolar pulse width modulation (PWM) with carrier interleaving angle of 180°. The proposed method reduces the ground leakage current by more than an order of magnitude. A novel modification to the LCL filter is proposed which further reduces the leakage current by 48%. It is shown that these modifications make the overall system insensitive to circuit non-idealities. Experimental results based on ground leakage current measurements on a 7.5 kW parallel single-phase PWM rectifier are presented. These results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A new phase coding is proposed to eliminate the continuous wave interference (CWI) in Loran navigation systems. In fact, CWI is one of the most important noise sources that make errors in signal phase tracking. Consequently, undesirable errors are constructed in time of arrival (TOA) measurement and ultimately navigation precision is reduced dramatically. The performance of Loran navigation systems is improved by applying the proposed phase coding and also using the averaging and phase decoding method. Analyses results show that if the interference is synchronous, then the proposed phase coding, called as Bayat-Madani phase code interval, cancels interference effects on TOA measurement completely. This interference cancelation is independent from the received signal signal-to-interference ratio. For near-synchronous and asynchronous CWI, the TOA error originated from interference is improved considerably, in some frequencies about 100 times, compared to the standard Loran. Furthermore, almost all of the sky multi-hops are eliminated as well. [ABSTRACT FROM AUTHOR]

A generalised direct matrix synthesis is proposed for microwave lossless filters with arbitrary phase shift at centre frequency and complex terminal impedances. The functions of traditional lossless filters, ideal phase shifters, and ideal impedance matching networks are thus substantially combined into one entity to provide an attractive technique for the realisation of compact narrowband microwave front-ends. The synthesis starts with a group of general S-parameters that consider both amplitude and phase responses as well as complex terminations for an Nth-order filter. A transversal array network incorporating resonators as well as non-resonating nodes is then introduced to accommodate the given S-parameters. In result, a canonical (N + 2) × (N + 2) coupling matrix with newly defined source–source and load–load couplings is generated. Some examples, including a fully canonical prototype and a mixed topology diplexer, are demonstrated to show the flexibility of the methodology. Moreover, an eighth-order coaxial cavity filter, with a −120° additional phase shift for S-parameters, is designed and fabricated. The measured results are well consistent with the synthesis ones, which validates the availability of this study in physical implementations. [ABSTRACT FROM AUTHOR]

In this study, a varactor-loaded slot-ring resonator (SRR) is investigated and applied in the design of tunable common-mode (CM) suppression filter for high-speed differential signals. Two tunable capacitors (realised by two kinds of varactors) with different values are symmetrically added to the SRR. Under the stepped-width structure of the SRR, the frequency-tuning principle is studied. It can be found that the fundamental resonant frequency ffund can be shifted up and down by properly controlling the respective values of the two loaded capacitors, i.e. bi-directional tuning. As a result, the tuning range of ffund can be greatly enlarged, approximately double that of the traditional tunable resonator. Meanwhile, the employed stepped-width SRR is useful not only for miniaturising the circuit size, but also further increasing the tuning range of ffund. By etching the proposed SRRs on the ground plane underneath the differential microstrip line, two wideband tunable CM-suppression filters using one and three SRR units, respectively, are designed, and their simulated and measured results showing good agreement are presented. It is found that the CM stopband frequency can be tuned from 0.78 to 1.52 GHz, while the differential signals still keep good signal integrity in eye-pattern observation. [ABSTRACT FROM AUTHOR]

Owing to less conduction and switching power losses, the recently proposed Aalborg inverter has high efficiency within a wide range of input DC voltage for single-phase DC/AC power conversion. In theory, the conduction power losses can be further decreased, if an LLCL-filter is adopted instead of an LCL-filter for a voltage source inverter, mainly due to the reduced inductance. The Aalborg inverter shows the characteristic of a current source inverter, when working in the ‘boost’ state. Whether the LLCL-filter can meet the control requirement of this type inverter needs to be further explored. In this study, the small signal analysis for the modified-LLCL-filter-based Aalborg inverter is addressed. Through the modelling, it can be proven that compared with the LCL-filter, the modified-LLCL-filter causes no extra control challenge for the Aalborg inverter, and therefore more inductance in the power loop can be safely saved as well as a complete smaller filter size. A 220 V/50 Hz, 2000 W prototype is used to demonstrate the theoretical analysis. [ABSTRACT FROM AUTHOR]

A spatially decoupled biasing circuit is proposed for the biasing of varactor diodes in a tunable staircase X-band suspended substrate filter. The biasing lines are vertically aligned with lines of zero electric field which are created by the symmetric capacitive loading of half-wave planar resonators. A prototype filter is designed and a tunable centre frequency of between 11.75 and 12.15 GHz is measured. [ABSTRACT FROM AUTHOR]

In grid-connected inverters, utilisation of an appropriate output filter is vital to improve power quality. However, the filter, which comprises of capacitor and inductor(s), should be cost effective. In this study, an LCL filter with non-linear inverter-side inductor is used to reduce the filter volume and cost. In order to harness the undesirable non-linear behaviour of the LCL filter's inductor, a new control scheme based on proportional-resonant controller is proposed. The control strategy is based on combinational feedback of inverter-side and grid-side currents, with online adaptive estimation of non-linear inductor. With this scheme, the harmonic compensators' gains can be reduced, while stability margins and dynamic response are improved. Therefore, while a cost-effective filter is used at the inverter output, acceptable total harmonic distortion is achieved. Experimental tests based on a 7 kW digital signal processor controlled prototype inverter are provided to verify the proposed control strategy for grid-connected inverters with LCL output filter benefiting from low-cost non-linear inductor. [ABSTRACT FROM AUTHOR]

Compared with the traditional L filters, the high order LCL and LLCL filters for grid integration of voltage source converters offer better switching harmonic attenuation even with smaller passive elements. However, the inherent resonance of the high order filters complicates the control of the converter and also the design of filter parameters, especially at presence of digital delays and grid impedance variations. This study proposes a simple design procedure for the LCL and the LLCL filters of a delay-based stabilised converter that satisfies the predefined constraints on the converter current ripple, grid current harmonics and the reactive power of the capacitor and at the same time, ensures adequate stability of the simple single loop current control against the resonance. Moreover, the effect of grid impedance on the filter performance and controller stability is taken into account, thus the proposed method is robust against a wide range of grid impedance variations. Experimental results for a 3 kW test rig under steady state and transient conditions confirm the effectiveness of the proposed filter design algorithm. [ABSTRACT FROM AUTHOR]

A magnetically coupled boost (MCB) converter with the enhanced equivalent series resistance (ESR) of the filter capacitor for DC microgrid applications has been presented in this study. The proposed MCB converter with enhanced ESR filter capacitor uses only four state variables and exhibits a fourth-order minimum phase behaviour because of the complete elimination of right half plane zero. The characteristic of displaying fourth-order minimum phase behaviour of the proposed MCB converter with the enhanced ESR filter capacitor makes the design and analysis simple. Closedloop operation of the proposed MCB converter with the enhanced ESR filter capacitor with photovoltaic input using maximum power point tracking has been carried out to verify its applicability in DC microgrid. Steady state and dynamic modelling of the MCB converter has been carried out to demonstrate its advantages. The proposed algorithm is validated on a 145 W prototype through simulation and experimentation. [ABSTRACT FROM AUTHOR]

In this study, novel compact filtennas with large tunable frequency band are proposed for cognitive radio (CR) applications. Tunability is achieved by integrating a tunable T-shaped and H-shaped bandpass filter with a planar ultrawideband monopole antenna. The T-shaped filter consists of a microstrip resonator loaded with a stub. The H-shaped filter is composed of two connected microstrip resonators. The proposed tuning technique for both filters is based on centrally loading the stub and the H-shaped with only a single varactor for miniaturisation. Increasing the varactor capacitance results in decreasing the even resonant mode of the resonator without affecting the dominant odd mode. Measurements results show that the proposed T-shaped and H-shaped filtennas are capable of tuning over a wide operating band of 1.68 and 1.73 GHz covering continuous bands for CR communication with 32.9% frequency tuning range (TR) from 4.26 to 5.94 GHz and with 36.7% frequency TR from 3.85 to 5.58 GHz, respectively. Moreover, the radiation patterns are stable over the operating frequency ranges. The frequency characteristics and radiation performance are successfully optimised using 3D full-wave electromagnetic simulator. The fabricated designs are measured for verification purposes. Good agreements are found between simulated and measured results. [ABSTRACT FROM AUTHOR]

A tunable bandpass filter with wide tuning range of both its centre frequency and bandwidth is presented. This type of filter is a key element in modern wideband and multiband systems. The proposed filter is based on short sections of two pairs of shunt connected parallel-coupled lines and short-ended stub resonators, which are tuned using varactor diodes. The structure has two resonant modes as well as one-side edge transmission zero that can be relocated and controlled for any desired position. A thorough theoretical analysis is utilised to find the initial values of the filter's design parameters and estimate its performance. To validate the proposed design and its theoretical analysis, two prototype filters are fabricated and tested. The measured results indicate wide tuning range ratios for the centre frequency and bandwidth of up to 2.85 (0.52 to 1.48 GHz) and up to 5.2 (55 to 285 MHz), respectively. The fabricated filters are compact with an overall size (in guided wavelengths at the centre frequency) of less than 0.06 × 0.16. [ABSTRACT FROM AUTHOR]

A broadband polarisation-independent circuit analogue absorber comprising multi-layer resistive frequency selective surfaces (FSS) has been presented in this study. The proposed structure consists of a periodic arrangement of square loops loaded with lumped resistors and these square loops are printed on dielectric substrates separated by an air spacer. The simulated result shows the reflectivity below -10 dB in the frequency range from 4.96 to 18.22 GHz (fractional bandwidth of 114.40%) under normal incidence, covering C, X, and Ku bands. An equivalent circuit analysis has been introduced to characterise the proposed absorber, which shows good matching with the full-wave analysis. The effects of the individual FSS layers and the air spacer have been studied and several parametric variations have been carried out to examine the sensitivity of the design parameters on the absorption bandwidth. Finally, the designed absorber has been fabricated and measured in anechoic chamber, which shows good agreement between the experimental results and the simulated responses, under different angles of incidence as well as for various polarisation angles. [ABSTRACT FROM AUTHOR]

To accurately design wideband filters composed of three-coupled-lines, an improved equivalent circuit is derived by taking the cross-coupling between non-adjacent lines into consideration. Since the cross-coupling between non-adjacent lines is also dependent on the coupling between adjacent lines, conventional synthesis techniques cannot be used directly. Instead, an improved synthesis scheme based on successive iterations is proposed to synthesise the filters. As examples, two 2-stage microstrip three-coupled-line filters [bandwidth: 2.67-5.33 GHz (fractional bandwidth: 67%)] with a reversed connection sequence are synthesised, simulated, and experimentally realised to validate the proposed theory. The frequency responses of the designed filters using the authors' new model and synthesis theory compare well with those by simulation and experiment, whereas an error of about 17% is found in bandwidth if the authors use the conventional model that neglecting the cross-coupling between non-adjacent lines. In addition, the asymmetric property of the three-line unit is revealed. [ABSTRACT FROM AUTHOR]

This study analyses the feasibility of a unique sliding-mode control law to regulate a bidirectional boost converter with output filter in a seamless manner. The output voltage of the converter is effectively regulated by means of a proportional-integral controller, while the inner current loop has a sliding-mode current controller. The stability of this converter is verified for both step-up and step-down operation modes, considering the converter is part of a determined powertrain arrangement for an electric vehicle. Simulation and experimental results have proven the stability of the system in both operating modes and also during transitions, confirming that sliding-mode control is an appropriate control strategy for a bidirectional boost converter with output filter. [ABSTRACT FROM AUTHOR]

Applications such as electrolysis, electrowinning, DC arc furnaces and plasma torches require high-current (several kA) power supplies at low-voltage levels (few hundreds of volts). In this study, conventional rectifier topologies (diode- and thyristor-based multi-pulse rectifiers with on-load tap changing transformer and chopper-rectifier) used for high-current, variable-voltage applications are reviewed along with recent advancements in the field. The main applications themselves are also discussed. Issues with conventional topologies are highlighted. Power quality techniques like passive and active filters are discussed for power factor and current harmonics compensation. Advanced medium- to high-frequency transformer-based topologies (with current and voltage source rectifiers) are discussed along with simulation results. [ABSTRACT FROM AUTHOR]

Use of LCL filter along with a voltage source inverter (VSI) requires damping of resonance. Active damping (AD) methods are preferable compared with passive damping methods from efficiency point of view. Recent researches show that achieving stable operation of a grid connected VSI with LCL filter at a low switching frequency to resonance frequency ratio can cause instability. In this study a resonant integrator (RI) based second order filter (RISF) has been proposed for AD of LCL filter resonance for stable operation at low switching frequency to resonance frequency ratio. The method extracts resonance frequency capacitor current from sensed capacitor voltage in a per phase manner and does not need any additional sensors. The modelling and analysis of the closed loop system with PR current controller and proposed AD has been carried out in discrete domain including all delay effects. Experimental results have been included in support of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Active filters are power electronics devices used to eliminate harmonics from the distribution network. This article presents an active disturbance rejection control scheme for active filters. The controller is based on a linear disturbance observer combined with a disturbance rejection scheme. The parameter tuning is based on a combined pole placement and an optimal estimation based on Kalman-Bucy filter. Proposed scheme is validated through simulation and experimental work in an active filter. [ABSTRACT FROM AUTHOR]