Abstract: This paper deals with reactive power compensation and harmonics elimination in medium-voltage industrial networks using a hybrid active power filter. It proposes a hybrid filter as a combination of a three-phase, two-level, voltage-source converter connected in parallel with the inductor of a shunt, single-tuned, passive filter. This topological structure greatly decreases the voltage and current stress over the elements of the active filter. Since the topology is composed of a single-tuned branch, the control algorithm also has to ensure sufficient filtering at other harmonic frequencies. We propose using a proportional-resonant, multiloop controller. Since the controller is implemented in a synchronous-reference frame, it allows us to use half the number of resonators, compared with the solution using proportional-integral controllers in the harmonic-reference frame. Theoretical analyses and simulation results obtained from an actual industrial network model in PSCAD verify the viability and effectiveness of the proposed hybrid filter. In addition, the simulation results are validated by a comparison with the results obtained from a real-time digital simulator.

Abstract: This study deals with the analysis and implementation of compensation algorithms applied to a shunt active power filter, which uses three single-phase full-bridge converters sharing the same dc-bus voltage. The shunt filter is applied to three-phase four-wire systems, performing harmonic current suppression, reactive power compensation and power factor improvement. In addition, load unbalances compensation is also carried out. Two different control strategies are presented. In the first strategy, which is called independent current control, the currents of the three-phase power source are independently compensated performing harmonic suppression and load reactive power compensation, that is, the three-phase four-wire system is treated as three independent single-phase systems. In the second strategy, in addition to harmonic suppression and load reactive power compensation, the shunt filter also performs load unbalance compensation, resulting in sinusoidal and balanced source currents. The compensating algorithms are evaluated by means of several experimental test conditions, in order to validate the theoretical development and analyse the performance of the shunt filter.

Abstract: In this paper, an alternative control method is proposed to improve the harmonic suppression efficiency of the active power filter in a distorted and an unbalanced power system to compensate for the perturbations caused by the unbalanced non-linear loads. The proposed method uses a self-tuning filter (STF) to process the grid voltage in order to provide a uniform reference voltage to obtain the correct angular position of the phase locked loop. Moreover, the required compensation currents are obtained by implementing another STF in the transformed set of currents in order to separate the fundamental and the harmonic currents. This allows the calculation of a precise reference current for the unbalanced, the non-linear and the variable load conditions. The proposed control method gives an adequate compensating current reference even for a non-ideal voltage and unbalanced current conditions. The real-time control of the filter under the distorted and the unbalanced power system is developed in an RT-LAB real-time platform. The results obtained in the software-in-the-loop configuration are presented to verify the effectiveness of the proposed control technique.

Abstract: This paper proposes an adaptive low-dc-link-voltage-controlled LC coupling hybrid active power filter ( LC-HAPF) with a neutral inductor, which can compensate both dynamic reactive power and current harmonics in three-phase four-wire distribution power systems. Due to its adaptive low-dc-link-voltage characteristic, it can obtain the least switching loss and switching noise and the best compensating performances, compared with the conventional fixed and newly adaptive dc-voltage-controlled LC-HAPFs. The design procedures of the dc-link voltage controller are discussed, so that the proportional and integral gains can be designed accordingly. Moreover, the general design procedures for the adaptive dc-voltage-controlled LC-HAPF with a neutral inductor are also given. The validity and effectiveness of the adaptive dc-link voltage-controlled LC -HAPF with a neutral inductor are confirmed by experimental results obtained from a 220-V 10-kVA laboratory prototype compared with the conventional fixed and adaptive dc-link voltage-controlled LC-HAPFs without a neutral inductor.

Abstract: This paper presents a new high-order filter for three-phase grid-connected voltage source converters (VSCs) named the inductor-trap-capacitor-inductor (LTCL) filter, in which multiple LC trap filters are inserted in parallel with the branch of the capacitor in the traditional LCL filter to compose multiple series resonant circuits at the selected frequencies. Particularly, the LTCL filter can attenuate the harmonic currents around the multiples of switching frequencies and guarantee -60 dB/decade attenuation in the high-frequency band, leading to a decrease of the total inductance and volume. Furthermore, within half of the switching frequency range, an LTCL -filter-based grid-connected VSC has almost the same frequency-response characteristic as that with the traditional LCL filter. That is to say, the LTCL filter does not bring any extra control difficulties. The basic parameter selection criteria and the parameter design procedure of the LTCL filter are introduced. Moreover, the sensitivity analysis of the LTCL filter is analyzed and discussed in detail. The comparative analysis and discussion considering the LCL filter, the LLCL filter, the multituned traps filter, and the proposed LTCL filter, have been presented and evaluated through the experiments on a 65-kW three-phase grid-connected VSC prototype.

Abstract: This paper proposes a solution for reducing the ground leakage current in transformerless single-phase grid-connected photovoltaic converters. This is obtained with the introduction of an active common-mode filter able to compensate for variations of the output common-mode voltage of the power converter. The active common-mode filter is applied to a widespread and efficient full-bridge driven by a three-level pulse width modulation, allowing the power converter to operate with low ground leakage current and with an arbitrary power factor. After showing the desired voltage waveform for common-mode voltage compensation, this paper presents the design guidelines for the needed additional magnetic component together with the power loss considerations for all the devices added for the proposed solution. Experimental results show the performance of the proposed solution in terms of ground leakage current reduction, effectiveness of dead-time compensation, total harmonic distortion of the injected grid current, and power losses.

Abstract: This paper presents a phase-locking control scheme based on artificial neural networks (ANNs) for active power filters (APFs). The proposed phase locking is achieved by estimating the fundamental supply frequency and by generating a phase-locking signal. The nonlinear-least-squares-based approach is modified to estimate the supply frequency. To improve the accuracy of frequency estimation, when the supply voltage contains harmonics that are not known, a prefiltering stage is introduced. In shunt APF applications, not only the information of frequency is sufficient but also the phase information of the supply voltage is required to generate a unit template that is phase-locked to the supply voltage. Therefore, in this paper, an adaptive-linear-neuron-based scheme is proposed to extract the phase information of the supply voltage. The estimated system frequency and phase information are then utilized to generate a phase-locking signal that assures a perfect synchronization with the fundamental supply voltage. To demonstrate the effectiveness of the proposed approach, the synchronous reference frame ( d-q theory) shunt APF control method with the proposed ANN-based phase-locking scheme is adopted. The performance of the proposed ANN-based approach is verified experimentally with different supply systems and load conditions.

Abstract: In this paper, we propose a discrete-time IIR low-pass filter that achieves a high-order of filtering through a charge-sharing rotation. Its sampling rate is then multiplied through pipelining. The first stage of the filter can operate in either a voltage-sampling or charge-sampling mode. It uses switches, capacitors and a simple gm-cell, rather than opamps, thus being compatible with digital nanoscale technology. In the voltage-sampling mode, the gm-cell is bypassed so the filter is fully passive. A 7th-order filter prototype operating at 800 MS/s sampling rate is implemented in TSMC 65 nm CMOS. Bandwidth of this filter is programmable between 400 kHz to 30 MHz with 100 dB maximum stop-band rejection. Its IIP3 is +21 dBm and the averaged spot noise is 4.57 nV/$surd$ Hz. It consumes 2 mW at 1.2 V and occupies 0.42 mm 2.

Abstract: This paper presents a simplified control technique for a dual three-phase topology of a unified power quality conditioner—iUPQC. The iUPQC is composed of two active filters, a series active filter and a shunt active filter (parallel active filter), used to eliminate harmonics and unbalances. Different from a conventional UPQC, the iUPQC has the series filter controlled as a sinusoidal current source and the shunt filter controlled as a sinusoidal voltage source. Therefore, the pulse width modulation (PWM) controls of the iUPQC deal with a well-known frequency spectrum, since it is controlled using voltage and current sinusoidal references, different from the conventional UPQC that is controlled using nonsinusoidal references. In this paper, the proposed design control, power flow analysis, and experimental results of the developed prototype are presented.

Abstract: This paper presents a universal active filter for harmonic and reactive power compensation for single-phase systems applications. The proposed system is a combination of parallel and series active filters without transformer. It is suitable for applications where size and weight are critical factors. The model of the system is derived and it is shown that the circulating current observed in the proposed active filter is an important quantity that must be controlled. A complete control system, including pulse-width modulation (PWM) techniques, is developed. Comparisons between the structures are made from weighted total harmonic distortion (WTHD). The steady-state analysis is also presented in order to demonstrate the possibility to obtain an optimum voltage angle reducing the current amplitude of both series and parallel converters and, consequently, the total losses of the system. Simulated and experimental results validate the theoretical considerations.

Abstract: This paper presents a robust direct single-loop current control scheme based on structured singular value (μ) minimization approach for induced-capacitor-inductor (LCL)-filtered distributed generation converters in grid-connected and isolated microgrid modes. Unlike the conventional $H_\infty$ -based approach, the proposed interface maintains perturbed system stability, under wide range of grid (or microgrid) impedance variation, without the application of any additional damping loops. Moreover, the performance of the perturbed system in terms of grid-voltage and harmonic disturbance rejection can be improved significantly by the adopted method. This is due to the less conservative nature of the μ-synthesis-based solution as it takes advantage of the additional structure introduced to the uncertainty block by the performance criteria. The salient features of the proposed controller are 1) single-loop direct current control of LCL -filtered converters with inherent damping of the LCL filter resonance without any need for additional damping loops; 2) robust stability and active damping performances by mitigating the LCL resonance under wide range of grid (or microgrid) impedance variation; 3) improving the performance of the current controller by removing its dependency on the grid-voltage feed-forward loop by providing high disturbance rejection feature against fundamental and harmonic voltage disturbances; 4) computationally efficient fixed-order structure with minimum sensor requirements (only grid-side currents are needed for feedback control). A comparative theoretical analysis, time-domain simulation results, and experimental test results are presented to show the effectiveness of the proposed control scheme.

Abstract: The harmful effects of harmonics are an important issue in wind power plants (WPPs), especially in offshore applications. In offshore WPPs, the wind turbines are linked to the network through high-power converters that produce harmonics at relative low frequencies. Moreover, in the network of a WPP, the propagation of noncharacteristic harmonics and the effect of resonance contribute as well in boosting the harmonic distortion. In this paper, a solution for compensating the harmonics in a WPP by means of using hybrid filters is proposed. In this paper, not only the filtering solution is tested, but also a method for finding the best place where to connect the filter, based on a modal analysis or a harmonic modal resonance analysis, is implemented. The proposed solution has been tested by considering the model of a real 400-MW offshore WPP as the study case. As it will be shown, the hybrid filter is capable of damping the resonances in the plant, while the analysis conducted permits us to optimize its location in the plant.

Abstract: Actively simulated grounded inductors have been used in several applications ranging from filter to oscillator design as well as cancelation of parasitic inductances. In this paper, new lossless grounded inductance simulator employing only one voltage differencing buffer amplifier (VDBA) and two passive components is proposed. The aim of this paper is to present new inductance simulator using the minimum number of active and passive components. The proposed inductance simulator can be tuned electronically by changing the transconductance of the VDBA. Finally, using the proposed inductance simulator a band-pass filter is constructed. The performance of the filter is simulated by using PSPICE and simulation results are verified experimentally.

Abstract: Level-shifted pulse-width modulation (LSPWM) technique for single-star bridge cells (SSBCs)-based modular multilevel cascade inverter (MMCI) produces better harmonic performance than the phase-shifted PWM (PSPWM) technique but its applications are limited because of the unequal device conduction periods, which is undesired in high-power applications. To evenly distribute the switching and conduction losses, the switching patterns should be rotated among the H-bridge cells. This study evaluates two possible carrier rotation techniques, which combines the advantages of uniform power distribution among H-bridge cells and equal device conduction periods from PSPWM technique and improved harmonic performance from LSPWM technique. The effectiveness of the two adopted techniques has been established through simulation and experimental studies. To verify the equality in devices conduction periods, algorithms have been proposed. Further, the behaviours of the DC capacitor voltages of individual H-bridges cells of a five-level SSBC-MMCI-based active power filter have been studied with the adopted carrier rotation techniques.

Abstract: In this paper, a vector fitting (VF) based analytical extraction method, which is capable of accurately extracting the coupling matrix and the uneven unloaded Qs of each electric resonators of a filter, is presented. Having had the complex poles and residues determined using VF, the coupling matrix can be obtained by a sequence of complex orthogonal transformations. As a side product, the unloaded Qs for each resonator will be directly obtained from the complex diagonal elements of the coupling matrix. To demonstrate the effectiveness of the proposed method, an ideal demonstrative example along with two practical challenging filter tuning examples, namely, an eight-pole dual-mode dielectric filter and an eight-pole dual-mode predistortion filter, are demonstrated. An excellent match between the responses of the measured data and those from the extracted coupling matrix with actual unloaded Q factors can be seen.

Abstract: This letter presents a novel integrated structure for electromagnetic interference (EMI) active filter. This approach integrates an active filter with a passive one to form a hybrid EMI filter. The chosen active filtering circuit is integrated on the printed board circuit embedding the integrated EMI choke. Theoretical and realization results show the integration compatibility between the active part and the passive part. Then, EMI measurements show that the proposed integrated hybrid filter can greatly reduce the noise at high and low frequencies while reducing the overall bulkiness.

Abstract: This letter investigates into the impedance interaction between the electromagnetic interference (EMI) filter and the noise propagation path, and its influences on the filter design. It proves that the impedance resonance in the propagation path decreases the filter's high-frequency in-circuit attenuation. This letter proposes a method to improve the filter's high-frequency performance using an impedance-mismatching filter. The impedance-mismatching filter damps the resonance in the common mode (CM) noise propagation path and eliminates the high-frequency noise spike. By applying this method in the filter design, the CM inductor of the EMI filter can be significantly reduced since the EMI filter avoids the overdesign caused by its high-frequency performance degradation, and the filter can potentially achieve high power density. This letter also proposed a design procedure for this impedance-mismatching filter. An improved EMI filter design method considering this impedance mismatching is also proposed in this letter.

Abstract: We present a comprehensive design, fabrication, and characterization analysis of compact silicon-on-insulator bandpass filters with widely tunable bandwidth. The filter architecture is based on an unbalanced Mach-Zehnder interferometer loaded with a pair of ring resonators. A wide bandwidth tunability (from 10% to 90% FSR) can be achieved by controlling the resonant frequency of the rings while preserving a good filter off-band rejection. Design rules are provided that take into account fabrication tolerances as well as losses. Furthermore, the use of tunable couplers allows a more flexible shaping of the spectral response of the filter. The sensitivity with respect to nonlinear effects is carefully investigated. Operation over a wavelength spectrum of 20 nm is demonstrated, making the device suitable for channel subset selection in WDM systems, reconfigurable filters for gridless networking and adaptive filtering of signals.

Abstract: A 0.4-V phase-locked loop (PLL) that has much improved power efficiency is realized in standard 65-nm CMOS. The PLL employs a novel ultralow-voltage charge pump that compensates current mismatch with an active loop filter and produces significantly reduced reference spurs. Its voltage-controlled oscillator (VCO) is designed with the body-bias technique and includes an automatic frequency calibration circuit that provides low VCO gain and wide tuning range. The PLL output frequency can be tuned from 90 to 350 MHz. At 350-MHz output, the PLL consumes 109 $\mu\hbox{W}$ , which corresponds to the power efficiency of 0.31 mW/GHz.

Abstract: This paper presents a novel hybrid output filter topology for the inverter-motor system. It is shown that the proposed filter drastically reduces the common mode (CM) voltage at the motor terminals. The proposed filter is composed of a conventional LC filter cascaded with an active motor CM impedance regulator. The active circuit, utilizing an integrated high-voltage op-amp, is very efficient in decreasing the motor CM equivalent capacitance, as well as damping the high common voltage on the motor terminal. Therefore, the motor impedance is also used as part of the filter, and the common voltage can be eliminated dynamically in the active impedance regulator by feedback control. Furthermore, the size of the passive filter can be reduced to a large extent. Experimental verification of the filter topology is provided with a laboratory system consisting of a 380-V inverter and a 0.37-kW induction motor.

Abstract: A novel circuit configuration for the realization of low power single-input three-output (SITO) current mode (CM) filters employing only MOS transistors are presented. The proposed circuit can realize low-pass (LP), band-pass (BP) and high-pass (HP) filter functions simultaneously at three high impedance outputs without changing configuration. Despite the other previously reported works, the proposed circuit is free from resistors and passive capacitors. Instead of passive capacitors; the gate-source capacitor of MOS transistor is used making the proposed circuit ideally suitable for integration. Compared to other works, the proposed filter has also the lowest number of transistors and lowest power consumption. The proposed circuit exhibits low-input and high-output impedances, which is highly desirable for cascading in CM signal processing. Moreover, it is center frequency can be electronically adjusted using a control current without a significant effect on quality factor (Q) granting it the highly desirable capability of electronic tunability. Transfer functions of the LP, BP and HP outputs are derived and the performance of the proposed circuit is proved through pre layout and post layout simulations at supply voltage of 1.8 V and using 0.18 μm CMOS process parameters. The power consumption and the required chip area are only 0.5 mW and 77.4 μm × 70.2 μm, respectively.

Abstract: A novel common-mode (CM) EMI active filter for dc-fed motor drives is proposed. The active filter performs both the compensation of the CM voltage at the motor input and the mitigation of the leakage high-frequency CM currents, thus increasing the drive reliability and the vehicle electromagnetic compatibility (EMC). The filter scheme is based on a voltage feedback action and also includes a feed-forward action by exploiting a suitably estimated CM current. An optimized design of the CM voltage detection/injection systems is implemented. Moreover, the active filter is supplied by a smaller voltage than the dc link value; this permits a more performing amplifier to be used. The active filter behavior is analyzed theoretically and its performance is assessed by experiments. The realized prototype shows a good efficiency and compactness.

Abstract: The widespread usage of load compensators for carrying out harmonic and reactive power compensation is constrained by cost and poor efficiency due to switching losses. Hence, it is customary to employ active harmonic filters for harmonic compensation only, while traditional methods comprising of thyristor-switched capacitors are used to carry out reactive power compensation. Load compensators based on one-cycle control (OCC) have gained considerable significance as they do not require the service of a phase-locked loop to synchronize with the utility grid. However, existing OCC-based load compensators do not have the capability to differentiate between the fundamental reactive component and harmonic components of the load currents. Hence, they cannot be employed for harmonic compensation alone as they end up compensating for reactive current as well, leading to an increase in the converter rating. In order to overcome the aforementioned limitation, an OCC-based shunt harmonic filter which is capable of compensating only the harmonic components of the load current is proposed in this paper. The viability of the proposed scheme is confirmed by performing detailed simulation studies and experimental validation.

Abstract: This paper discusses the dynamic interaction of multi active power filters (APFs) paralleled with a weak power grid. In order to analyze the dynamic interaction from multi APFs, the output impedance of an APF is solved. The influences of both circuit and control parameters on the output impedance are analyzed. Based on the output impedance of an APF, the dynamic influences of an APF on the other APF connected to the weak grid are discussed. As shown in this paper, the stability of an APF is improved with an increased output filter inductance and some control parameters to reduce its bandwidth. The proposed analysis methods can be used not only for multi APFs but also for the other multi-inverters connected to a weak grid. Experimental tests are carried out using two paralleled three-phase 10-kVA inverters to confirm the validity of the theoretical analysis.

Abstract: This paper deals with a single-input multipleoutput biquadratic filter providing three functions (lowpass, high-pass and band-pass) based on voltage differencing differential input buffered amplifier (VD-DIBA). The quality factor and pole frequency can be electronically tuned via the bias current. The proposed circuit uses two VD-DIBAs and two grounded capacitors without any external resistors, which is suitable to further develop into an integrated circuit. Moreover, the circuit possesses high input impedance, providing easy voltage-mode cascading. It is shown that the filter structure can be easily extended to multi-input filter without any additional components, providing also all-pass and band-reject properties. The PSPICE simulation results are included, verifying the key characteristics of the proposed filter. The given results agree well with the theoretical presumptions.

Abstract: Dynamic behavior of the harmonic detection part of an active power filter (APF) has an essential role in filter compensation performances during transient conditions. Instantaneous power (p?q) theory is extensively used to design harmonic detectors for active filters. Large overshoot of p?q theory method deteriorates filter response at a large and rapid load change. In this study the harmonic estimation of an APF during transient conditions for balanced three-phase nonlinear loads is conducted. A novel fuzzy instantaneous power (FIP) theory is proposed to improve conventional p?q theory dynamic performances during transient conditions to adapt automatically to any random and rapid nonlinear load change. Adding fuzzy rules in p?q theory improves the decomposition of the alternating current components of active and reactive power signals and develops correct reference during rapid and random current variation. Modifying p?q theory internal high-pass filter performance using fuzzy rules without any drawback is a prospect. In the simulated system using MATLAB/SIMULINK, the shunt active filter is connected to a rapidly time-varying nonlinear load. The harmonic detection parts of the shunt active filter are developed for FIP theory-based and p?q theory-based algorithms. The harmonic detector hardware is also developed using the TMS320F28335 digital signal processor and connected to a laboratory nonlinear load. The software is developed for FIP theory-based and p?q theory-based algorithms. The simulation and experimental tests results verify the ability of the new technique in harmonic detection of rapid changing nonlinear loads.

Abstract: Artificial neural network (ANN) is a computational algorithm based on the structure and functions of biological neural networks. It is used for modelling of the non-linear systems that cannot be mathematically expressed by the formula and extraction of the system dynamics, expressed by using the complex mathematical equations, such as harmonics. To show the effective usage of ANNs in the power system, the fundamental harmonic of a load with six-pulse thyristor controlled rectifier is extracted with ANN by using the system variables that are difficult to express with each other. Then, a new approach is proposed to generate the reference signal for compensating the harmonics of the current by using discrete fuzzy logic in this study. In addition, a simple and useful method to determine the circuit parameters of the active power filter (APF) is proposed to reduce the rating of the required filter and the capacitor values without affecting its efficiency. Case studies are performed to test the performance of the proposed control algorithm for APF.

Abstract: A fast-transient repetitive control strategy for a three-phase shunt active power filter is presented in this study to improve dynamic performance without sacrificing steady-state accuracy. The proposed approach requires one-sixth of the fundamental period required by conventional repetitive control methods as the repetitive control time delay in the synchronous reference frames. Therefore, the proposed method allows the system to achieve a fast dynamic response, and the program occupies minimal storage space. A proportional-integral regulator is also added to the current control loop to eliminate arbitrary-order harmonics and ensure system stability under severe harmonic distortion conditions. The design process of the corrector in the fast-transient repetitive controller is also presented in detail. The LCL filter resonance problem is avoided by the appropriately designed corrector, which increases the margin of system stability and maintains the original compensation current tracking accuracy. Finally, experimental results are presented to verify the feasibility of the proposed strategy.