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Torque fluctuations in drivetrains are the result of dynamic excitations and can be unfavorable for the lifetime of the system. Passive ripple suppression methods exist, such as torsional dampers and flywheels, which are often bulky and not always desired. Alternatively, performant active control methods exist; however, their applicability to certain drivetrains is not covered. Therefore, this paper focuses on active control from a mechanical perspective, more specifically, drivetrain dynamics impacting active control effectiveness. A quasi-resonant controller is implemented as an active control method, and its performance and robustness are proven both in simulation on a 3-DOF mechanical model and experimentally at different excitation frequencies. The tests show that active control effectiveness is highly drivetrain-dependent. In particular, the propagation of the torque oscillation is influenced by the elastic filtering properties of the drivetrain, and the speed ripple depends on the inertial attenuation of the drivetrain. High-stiffness, low-inertia drivetrains benefit best from active control for ripple suppression because the inertial attenuation is limited, while high-stiffness elements increase the mechanical bandwidth before dynamic decoupling happens between the inertias of interest. Active control serves as a viable alternative for speed ripple reduction when drivetrain compactness is key, instead of the current passive solutions. [ABSTRACT FROM AUTHOR]

Torque fluctuations in drivetrains are the result of dynamic excitations and can be unfavorable for the lifetime of the system. Passive ripple suppression methods exist, such as torsional dampers and flywheels, which are often bulky and not always desired. Alternatively, performant active control methods exist; however, their applicability to certain drivetrains is not covered. Therefore, this paper focuses on active control from a mechanical perspective, more specifically, drivetrain dynamics impacting active control effectiveness. A quasi-resonant controller is implemented as an active control method, and its performance and robustness are proven both in simulation on a 3-DOF mechanical model and experimentally at different excitation frequencies. The tests show that active control effectiveness is highly drivetrain-dependent. In particular, the propagation of the torque oscillation is influenced by the elastic filtering properties of the drivetrain, and the speed ripple depends on the inertial attenuation of the drivetrain. High-stiffness, low-inertia drivetrains benefit best from active control for ripple suppression because the inertial attenuation is limited, while high-stiffness elements increase the mechanical bandwidth before dynamic decoupling happens between the inertias of interest. Active control serves as a viable alternative for speed ripple reduction when drivetrain compactness is key, instead of the current passive solutions.

Cascaded H-bridge drives require using a significant-size capacitor on each cell to deal with the oscillatory power generated by the H-bridge inverter in the DC-link. This results in a bulky cell with reduced reliability due to the circulating second harmonic current through the DC-link capacitors. In this article, a control strategy based on a finite control set model predictive control and a proportional-resonant controller is proposed to compensate for the oscillatory power required by the H-bridge inverter through the cell's input rectifier. With the proposed strategy, a DC-link second harmonic free operation is achieved, allowing for the possibility of reducing the capacitor size and, in consequence, the cell dimensions. The feasibility of the proposed control scheme is verified by experimental results in one cell of a cascade H-bridge inverter achieving an operation with a capacitance 141 times smaller than required by conventional control approaches for the same voltage ripple. [ABSTRACT FROM AUTHOR]

Introduction: The proportional resonant (PR) controller is known for its ability to effectively regulate sinusoidal current and voltage with low steady-state error. However, in the context of digital power systems, where operations are discrete in time, applying conventional PR controllers directly presents challenges. This study investigates the impact of various discretization methods on the performance of PR controllers, particularly under scenarios with varying reference frequencies.Methods: To assess the performance of digital PR controllers under varying reference frequency conditions, three discretization techniques are employed: zero-order hold (ZOH), impulse invariant (II), and zero pole matching (ZPM), in addition to the conventional deadbeat controller. These controllers are tested in conjunction with a single-phase pulse-width modulated (PWM) inverter, which is a crucial component in modern power systems.Results: Simulation results indicate the effectiveness of the different digital PR controllers in tracking both fixed and variable reference frequency signals while minimizing total harmonic distortion (THD) and steady-state error. When utilizing only the deadbeat controller, steady-state error and THD are measured at 4.9 V and 4.82%, respectively. However, the proposed ZPM-based digital PR controller significantly improves performance, reducing steady-state error to 0.12 V and THD to 0.45%, highlighting its superior performance.Discussion: The findings of this study emphasize the importance of choosing the appropriate discretization method when implementing PR controllers in digital power systems. The ZPM-based digital PR controller proves to be highly efficient in regulating power converters under varying grid frequency conditions. This research contributes to the understanding of digital PR controller behavior and its potential for improving power system performance, especially in scenarios with intermittent renewable energy resources and fluctuating grid frequencies.

Distorted voltage supplied as unbalanced and/or non-constant frequency can be found in weak grids, such as microgrids, or systems working in islanding mode. These kinds of systems are more sensitive under load changes. Particularly, an unbalanced voltage supply may be produced for large, single-phase loads. On the other hand, the connection/disconnection of high current loads may lead to important frequency variation, especially in weak grids where the short circuit current capacity is reduced. These conditions make the control of the power converter a more difficult task, because of the variations in the frequency and unbalancing. To address these issues, this paper proposes a resonant control algorithm to deal with variations in the voltage amplitude as well as grid frequency when a distorted power supply is considered. The frequency variation is an important drawback for resonant control because the resonance must be tuned at the grid frequency. This issue is overcome by using a variable sampling frequency in order to avoid re-tuning the controller parameters. On the other hand, under unbalanced conditions, the proposed method relaxes the phase with lower voltage amplitude by taking more power from the other phases in order to help the stability of the grid supply. To corroborate the mathematical analysis and the proposed control, a stability study is performed, including experimental and simulated results. [ABSTRACT FROM AUTHOR]

Electric machines are highly efficient and highly controllable actuators, but they do still suffer from a number of imperfections. One of them is torque ripple, which introduces high frequency harmonics into the motion. One (cost- and performance-neutral) countermeasure is to apply control that counters the torque ripple. This paper compares several single-input single-output (SISO) control approaches for feedback control of torque ripple of a Permanent Magnet Synchronous Machine (PMSM). The baseline is PI (proportional-integral) control, which does not suppress torque ripple, and the most popular control approach is proportional-integral resonant (PIR) control. Both are compared to an advanced PIR controller (PIRA), frequency modulation, a mixed sensitivity design, and an iterative learning controller (ILC). The analysis demonstrates that PIR control, mixed sensitivity state feedback, and the modulating controller achieve identical behaviour. The choice between these three options is therefore dependent on preferences for the design methodology, or on implementation factors. The PIRA and the ILC on the other hand show more sophisticated behaviour that may be advantageous for certain applications, at the expense of higher complexity. [ABSTRACT FROM AUTHOR]

The elimination of periodic torque disturbance in permanent magnet synchronous machine (PMSM) drives is a multifrequency control task, and adding resonant parts to the controller has an impact on the robustness of the system. This article aims to address the torque-ripple reduction in PMSM drives for smooth speed control, where an extended harmonic state observer (EHSO) is designed for estimation and attenuation of the selective periodic disturbance. The defects of applying the conventional bandwidth-parameterization method to the harmonic disturbance observer are explored. To improve the disturbance-rejection capability and the relative stability, a pole-placement strategy is proposed and analyzed through sensitivity function, which can preserve the comparable dynamic performance as the conventional extended state observer at the low-frequency range. The proposed EHSO also features easy parameter tuning and a modular structure for multiple harmonic disturbance rejection. Finally, the proposed method is evaluated on a laboratory PMSM platform. [ABSTRACT FROM AUTHOR]

Cascaded H-bridge drives require using a significant-size capacitor on each cell to deal with the oscillatory power generated by the H-bridge inverter in the DC-link. This results in a bulky cell with reduced reliability due to the circulating second harmonic current through the DC-link capacitors. In this article, a control strategy based on a finite control set model predictive control and a proportional-resonant controller is proposed to compensate for the oscillatory power required by the H-bridge inverter through the cell’s input rectifier. With the proposed strategy, a DC-link second harmonic free operation is achieved, allowing for the possibility of reducing the capacitor size and, in consequence, the cell dimensions. The feasibility of the proposed control scheme is verified by experimental results in one cell of a cascade H-bridge inverter achieving an operation with a capacitance 141 times smaller than required by conventional control approaches for the same voltage ripple.

This paper addresses the periodic position tracking and load force disturbance rejection in linear permanent magnet synchronous motors (LPMSM). Periodic position tracking is a challenge for LPMSMs, as there are electromagnetic forces that are not uniform along the actuator stroke due to end effects, which can lead to position variations. The proposed control structure combines a proportional–integral (PI) controller in the direct-axis control loop and a modified PI plus a multiple resonant controller (PI-RES) in the quadrature-axis control loop to ensure periodic reference tracking and disturbance rejection. The controller design is carried out by solving a convex optimization problem under linear matrix inequality (LMI) constraints, which guarantee closed-loop stability and transient performance. Simulations and experimental results are performed using a dual quasi-Halbach permanent magnet array linear tubular actuator with a coreless moving armature. The effectiveness of the proposed method is evaluated by applying position reference signals with different frequencies and harmonic compositions in conjunction with two types of load force disturbances. Experiments show the proposed controller results in precise reference tracking with negligible steady-state error. [ABSTRACT FROM AUTHOR]

Distorted voltage supplied as unbalanced and/or non-constant frequency can be found in weak grids, such as microgrids, or systems working in islanding mode. These kinds of systems are more sensitive under load changes. Particularly, an unbalanced voltage supply may be produced for large, single-phase loads. On the other hand, the connection/disconnection of high current loads may lead to important frequency variation, especially in weak grids where the short circuit current capacity is reduced. These conditions make the control of the power converter a more difficult task, because of the variations in the frequency and unbalancing. To address these issues, this paper proposes a resonant control algorithm to deal with variations in the voltage amplitude as well as grid frequency when a distorted power supply is considered. The frequency variation is an important drawback for resonant control because the resonance must be tuned at the grid frequency. This issue is overcome by using a variable sampling frequency in order to avoid re-tuning the controller parameters. On the other hand, under unbalanced conditions, the proposed method relaxes the phase with lower voltage amplitude by taking more power from the other phases in order to help the stability of the grid supply. To corroborate the mathematical analysis and the proposed control, a stability study is performed, including experimental and simulated results.

Uninterruptible power supply (UPS) is an electronic power device that delivers voltage to critical loads and whose application must satisfy standardized performance requirements. Usual control techniques demand the UPS model. In this article, we propose a simple, model-free procedure based on the generalized forced oscillation method to design the control system of a UPS output stage. The procedure involves the design of an inner current loop with a proportional gain and a proportional-multiresonant controller in the output voltage loop. We also compare the closed-loop results obtained in a single-phase 3.5 kVA UPS with the IEC 62040-3 performance criteria and show that the results are equivalent to model-based approaches. [ABSTRACT FROM AUTHOR]

The long duration test of electrical equipment is an important tool for users and manufacturers to determine precise information as, for example, equipment operational limits, lifespan, thermal behavior, etc. Although useful, these long duration tests are usually conducted using passive elements such as in the burn-in test, consuming a great amount of energy and with limited flexibility to emulate different loading profiles (e.g., current and voltage levels, harmonics content, etc.). In this context, to perform tests in power transformer emulating its real operation conditions can be a difficult task, since the standards procedures do not emulate the loading levels and the burn-in test consumes a high quantity of energy. Moreover, in distribution networks, the transformers are submitted to an increasing level of nonlinear voltage and current. Thus, it is important to test them under these conditions. The use of active electronic loads (AEL) is an alternative to solve these problems since the device structure can have regenerative proprieties and its control can emulate different types of load. This paper presents an AEL to perform tests in power transformers with low energy consumption that is capable of imposing controlled voltage and current (frequency, level, and harmonic distortion) to the transformer under test. The proposed methodology is validated by experimental results of a 50 kVA prototype.

When targeting mission critical applications, the design of the electronic actuation systems needs to consider many requirements and constraints not typical in standard industrial applications. One of these is tolerance to faults, as the unplanned shutdown of a critical subsystem, if not handled correctly, could lead to financial harm, environmental disaster, or even loss of life. One way this can be avoided is through the design of an electric drive systems based on multi-phase machines that can keep operating, albeit with degraded performance, in a partial configuration under fault conditions. Distributed architectures are uniquely suited to meet these challenges, by providing a large degree of isolation between the various components. This paper presents a system architecture suitable for scalable and high-performance fault tolerant machine drive systems. the effectiveness of this system is demonstrated through theoretical analysis and experimental verification on a six-phase machine.

Electric machines are highly efficient and highly controllable actuators, but they do still suffer from a number of imperfections. One of them is torque ripple, which introduces high frequency harmonics into the motion. One (cost- and performance-neutral) countermeasure is to apply control that counters the torque ripple. This paper compares several single-input single-output (SISO) control approaches for feedback control of torque ripple of a Permanent Magnet Synchronous Machine (PMSM). The baseline is PI (proportional-integral) control, which does not suppress torque ripple, and the most popular control approach is proportional-integral resonant (PIR) control. Both are compared to an advanced PIR controller (PIRA), frequency modulation, a mixed sensitivity design, and an iterative learning controller (ILC). The analysis demonstrates that PIR control, mixed sensitivity state feedback, and the modulating controller achieve identical behaviour. The choice between these three options is therefore dependent on preferences for the design methodology, or on implementation factors. The PIRA and the ILC on the other hand show more sophisticated behaviour that may be advantageous for certain applications, at the expense of higher complexity.

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Over the last few decades, the consolidated goal of reducing greenhouse gasses has increased the relevance of renewable energy research, electromobility, energy storage, and distributed generation, micro-grids, among others. Micro-grids, systems working in islanding mode, are particular cases where some disadvantages are present due to the wide variations which may appear across their electrical quantities. Variations on the voltage amplitude and the frequency are intrinsic in the operation of weak grids, because they have low inertia and therefore the load must be able to cope with these variations, otherwise loads may trip electrical system protection. Particularly, on power electronic drives, these frequency deviations will lead to increased system nonlinearities, entailing a more critical controller design. To overcome these issues, this paper presents an implementation of a resonant controller with self-tuned gains. The strategy imposes a constant sampling time which allows these controllers to be used in variable frequency environments. In addition, the computational capacity required for the digital board is also considered. The simulated and experimental results provided demonstrate the good performance of this proposal.

As for a grid-connected PWM converter with LCL filter, harmonic current can flow freely into the grid-side inductor and filter capacitor, when the connected power grid is harmonically distorted. The fact lies in that the conventional control scheme has a little ability to suppress the grid current harmonics. Though the harmonics can be suppressed by the capacitor current compensation method, it may lead to system stability issues. This paper proposes an improved harmonic suppression scheme with the partial capacitor current feedforward, which can effectively suppress the specified grid current harmonics on the premise of ensuring the system stability. Since the partial capacitor current is obtained as the differential output of a multi-second-order generalized integrator, no extra current sensors are needed. The effectiveness and feasibility of the proposed strategy are verified by detailed experimental results.

This paper investigates an adaptive combined control strategy for single-phase cascaded H-bridge multilevel converter under distorted load conditions. The nonlinear loads cause harmonic distortion and affect the quality of output voltage. An adaptive voltage control strategy is suggested to compensate for the harmonic distortion caused by the nonlinear loads. The suggested control strategy enables the output voltage to track the reference according to the load-side disturbances. The DC links of the multilevel converter generate low-frequency ripples which also cause output voltage distortion under nonlinear load conditions. To compensate this, an adaptive DC link ripple control strategy is also suggested. Detailed analysis has been conducted to verify the effectiveness of the suggested system and is compared to the conventional control strategies. Fast dynamic response and lower distortion in output voltage are obtained with the suggested strategy compared to the conventional control strategies. Experimental and simulation results are provided to validate the suggested control scheme. [ABSTRACT FROM AUTHOR]

Performance degradation is, in general, regarded as a power quality problem. One solution to recover grid performance is through the application of a unified power quality conditioner (UPQC). Although these devices are multi-input/multi-output (MIMO) systems, the most common control strategies consist of two decoupled controllers, which neglect the coupling effects and add uncertainty to the system. For this reason, this paper proposes a multivariable resonant observer-based control strategy of a UPQC system. This method includes all significant coupling effects between this system and the grid. This strategy results in a stability-based compensator, which differs from recently proposed strategies that are based on signal calculation and cannot assure closed-loop stability. In addition, this paper introduces a simplified controller tuning strategy based on optimal conventional methods without losing closed-loop performance. It implies that the controller can be easily tuned, despite the complexity of the MIMO dynamic model. The UPQC with the resonant observer is verified on an experimental setup for a single-phase system, obtaining three relevant results for power quality improvement: (1) harmonics compensation tested with a total harmonic distortion limit of 5%; (2) sags and swells mitigation; and (3) power factor correction, achieving a unitary value on the grid side.

Resonant controller (RSC) is one of the most popular approaches for ac current/voltage control due to the high performance of zero steady-state tracking error. However, it suffers from heavy computational burden issue when multiple RSCs are demanded to control multiple harmonics. To alleviate this issue, a down-sampled multirate RSCs (MRRSCs) scheme is proposed for controlling power inverters, e.g., grid-connected inverters and active power filters. The proposed control scheme is composed of an inner control loop with a fast sampling rate, which is identical to the switching frequency, and an array of paralleled MRRSCs-based external control loop with a reduced sampling rate. With the reduced sample rate, the MRRSCs can be executed alternatively in the dq-frame, such that the computational burden can be significantly reduced per cycle. Moreover, to reinforce the wide frequency adaptability of the MRRSC, its central resonant frequency is online updated according to the output of the phase-locked loop. In the paper, the equivalent single-rate closed-loop model of the overall system is developed, based on which the controller parameters are designed employing the Nyquist diagram and root locus. Finally, experiments are performed on a grid-connected inverter to validate the superiority of the proposed scheme. [ABSTRACT FROM AUTHOR]

AC current regulators are susceptible to controller windup, i.e., the condition in which the controller dynamic states ramp the controller output up to very large values when the commanded reference cannot be achieved because of inverter saturation. Recovering from saturation can take considerable time once the linear mode has been restored, which degrades the current regulator's transient performance and can also impact on its stability. This paper proposes an improved formulation using the concept of signal conditioning, where windup is avoided by feeding the controller states entirely from the constrained inverter pulsewidth modulation command. Unlike previous approaches, this technique has the benefit of a simplified realization, since the controller transfer functions do not require algebraic reformulation. This makes it particularly suitable for multiple cascaded resonators used in harmonic compensation systems. The technique has been validated using simulation and experimental investigations for a grid-connected inverter. [ABSTRACT FROM AUTHOR]

To improve power density and motor performance, new bearingless motor topologies combine torque and magnetic suspension coils into a single winding. Of these topologies, the parallel dual-purpose no-voltage winding is advantageous from the bearingless drive perspective because it requires the least amount of hardware. However, this topology can result in undesirable current controller performance from cross-coupling effects between the suspension and torque operation. This paper investigates these cross-coupling effects using rotating reference frame theory to derive relevant system disturbance transfer functions. The nature of this coupling is explained in relation to the machine and control parameters (inductances, resistances, controller gains) to provide insights for bearingless machine and control designers. The paper proposes and simulates different compensation techniques to minimize or eliminate the cross-coupling. It is shown that with careful machine design or with proper feedback control compensation, the motor controller can be implemented as a conventional motor drive, without knowledge of the magnetic suspension system. Finally, experimental validation is provided via two prototype machines. [ABSTRACT FROM AUTHOR]

This paper concentrates on a robust resonant control strategy of a permanent magnet synchronous motor (PMSM) for electric drivers with model uncertainties and external disturbances to improve the control performance of the current loop. Firstly, to reduce the torque ripple of PMSM, the resonant controller with fractional order (FO) calculus is introduced. Then, a robust two degrees-of-freedom (Robust-TDOF) control strategy was designed based on the modified resonant controller. Finally, by combining the two control methods, this study proposes an enhanced Robust-TDOF regulation method, named as the robust two degrees-of-freedom resonant controller (Robust-TDOFR), to guarantee the robustness of model uncertainty and to further improve the performance with minimized periodic torque ripples. Meanwhile, a tuning method was constructed followed by stability and robust stability analysis. Furthermore, the proposed Robust-TDOFR control method was applied in the current loop of a PMSM to suppress the periodic current harmonics caused by non-ideal factors of inverter and current measurement errors. Finally, simulations and experiments were performed to validate our control strategy. The simulation and experimental results showed that the THDs (total harmonic distortion) of phase current decreased to a level of 0.69% and 5.79% in the two testing environments.

In this paper, a two-degrees-of-freedom control structure is proposed to minimize both total harmonic distortion and tracking error of inverter output voltage, adopting a resonant tracking controller and a modified uncertainty and disturbance estimator (UDE). Owing to the two-degrees-of-freedom feature of the proposed control strategy, tracking and disturbance rejection tasks are decoupled and treated almost independently. A time-delay action is introduced into a commonly adopted low-pass UDE filter to minimize the output impedance magnitude around the odd harmonics, which is typical to nonlinear loads. Once the disturbance is properly rejected, a tracking resonant controller is designed to force the output of the nominal system to follow a sinusoidal reference with near-zero amplitude and phase error. The performance of the proposed control structure is fully verified by the experimental results. [ABSTRACT FROM AUTHOR]

In order to prevent the power switching devices (e.g., an insulated-gate bipolar transistor, IGBT) from shoot-through in voltage-source converters during a switching period, the dead time is added either in the hardware driver circuits of the IGBTs or implemented in software in pulse width modulation (PWM) schemes. Both solutions will contribute to a degradation of the injected current quality. As a consequence, the harmonics induced by the dead time (referred to as “dead-time harmonics” hereafter) have to be compensated in order to achieve a satisfactory current quality, as required by standards. In this paper, the emission mechanism of dead-time harmonics in single-phase PWM inverters is, thus, presented considering the modulation schemes in detail. More importantly, a repetitive controller has been adopted to eliminate the dead-time effect in single-phase grid-connected PWM converters. The repetitive controller has been plugged into a proportional-resonant-based fundamental-frequency current controller so as to mitigate the dead-time harmonics and also to maintain the control of the fundamental-frequency grid current in terms of dynamics. Simulations and experiments are provided, which confirm that the repetitive controller can effectively compensate the dead-time harmonics and other low-order distortions, and also, it is a simple method without hardware modifications. [ABSTRACT FROM AUTHOR]

This paper proposes a new control structure based on the parallel interconnection of a filtered repetitive controller and a resonant structure applied to uninterruptible power supplies — UPS. In particular, the filter in series with the repetitive controller adjusts the phase angle between resonant and repetitive loops, improving in this way the tracking performance. A particular filter structure is proposed, and an augmented state formulation is derived. Controller design is then carried out by the solution of an optimization problem with linear matrix inequalities constraints. Experimental results on a commercial 3.5kVA UPS illustrate the closed-loop performance. [ABSTRACT FROM AUTHOR]

The dc offset and scaling errors in the voltage measurements cause the injection of undesired dc and harmonic currents into the three-phase output currents of the grid-connected inverter. This study proposes an enhanced current control scheme to eliminate the dc and harmonic currents caused by voltage distortion and voltage measurement error in three-phase grid-connected inverters. The proposed current controller is designed in the synchronous (d-q ) reference frame and composed of a proportional resonant (PR) controller and a repetitive controller (RC). The role of the RC is to regulate the grid current follow the reference value as well as compensate all 6\rmn\omega {\rm{s}} and (6\rmn\pm 2)\omega{\rm{s}}\,(n= 1,\,2,\,3,\ldots) harmonic components caused by distorted grid voltage and scaling errors. Meanwhile, the PR controller helps to compensate the dc current generated by dc offset measurement errors to guarantee that the three-phase grid currents are balanced and sinusoidal with extremely low dc component. Since the RC employed in the proposed current controller reduces to time delay by four times compared to the conventional RC, the proposed control system ensures good steady-state performance of the grid current without deteriorating its fast dynamic response. The effectiveness of the suggested solution is verified by various experimental tests. [ABSTRACT FROM AUTHOR]

It was found that thermoacoustic solar-power generators with resonant control are more powerful than passive ones. To continue the work, this paper focuses on the synthesis of robustly resonant controllers that guarantee single-mode resonance not only in steady states, but also in transient states when modelling uncertainties happen and working temperature temporally varies. Here the control synthesis is based on the loop shifting and the frequency-domain identification in advance thereof. Frequency-domain identification is performed to modify the mathematical modelling and to identify the most powerful mode, so that the DSP-based feedback controller can online pitch the engine to the most powerful resonant-frequency robustly and accurately. Moreover, this paper develops two control tools, the higher-order van-der-Pol oscillator and the principle of Dynamical Equilibrium, to assist in system identification and feedback synthesis, respectively.

This paper focuses on the low-cost configuration of the lateral active suspension system for the high-speed train. First, the full-scale railway vehicle dynamics with 17-degree-of-freedom are introduced, where the actuator saturation, suspension deflection, and random and periodic track irregularities are considered. Then, based on the internal model principle, some classic active vibration control methods, e.g., the PID, positive position feedback, repetitive, and resonant controls, are unified as an internal model (IM)-based form and an IM-based resonant control is further presented. After that, to suppress various vibrations, three principles are presented to set the damping ratio and natural frequency of the IM-based resonant controller according to the properties of the controlled plant and/or the external disturbances. In consequence, an active suspension with the IM-based resonant controller is designed to improve the ride quality of the high-speed train, where the H\infty method is used to calculate the unique gain. Moreover, the configuration of the active suspension is low cost and consists of two independent control systems, where one control system only has a pair of actuators and an accelerometer. Finally, the random and periodic track irregularities are employed to show the efficiency of the proposed resonant-control-based active suspension by comparing with the linear quadratic Gaussian (LQG) and H\infty controllers. [ABSTRACT FROM PUBLISHER]

The operation of active power filters (APFs) under nonideal grid conditions, such as grid-frequency fluctuation and voltage harmonics, can lead to significant degradation in harmonic compensation performance. This paper proposes an adaptive digital-control scheme for a three-phase APF for use in harmonically distorted and variable-frequency grid conditions. This scheme is comprised of a grid-frequency adaptive resonant current controller and an enhanced synchronous-reference-frame phase-locked loop (SRF-PLL). The PLL uses an inherently stable adaptive-filtering stage to improve grid phase and frequency estimates in the presence of voltage harmonics. The improved PLL frequency estimate is used to update the resonant gains of a PI + vector-proportional-integral current-control scheme, implemented in the SRF. This enables the APF to maintain optimal performance in distorted grid conditions. The performance of the proposed APF control scheme is evaluated in a test microgrid, with a 15-kVA three-phase voltage-source converter configured as the APF, a 90-kVA grid emulator utilized to replicate distorted grid conditions, and a load emulator implemented to draw harmonic currents. The control scheme presented here is shown to demonstrate significant performance improvements under nonideal grid conditions compared with equivalent adaptive and nonadaptive methods. [ABSTRACT FROM PUBLISHER]

An integral plus resonant sliding mode direct power control (IRSMC DPC) strategy for voltage source converter high voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions is proposed in this paper. Through detailed instantaneous power flow analysis, a generalized power compensation method, by which the ratio between the amplitude of active and reactive power ripples can be controlled continuously, is obtained. This enables the system to provide flexible power control, so that the desired performance of the system on both the ac and dc sides can be attained under different operating conditions. When the grid voltage is unbalanced, one or both of the active and reactive power terms contain ripples, oscillating at twice the grid frequency, to obtain non-distorted ac current. A power controller consisting of the proportional, integral and resonant control laws is designed using the sliding mode control approach, to achieve accurate power control objective. Simulation studies on a two-terminal VSC-HVDC system using MATLAB/SIMULINK (R2013b, Mathworks, Natick, MA, USA) are conducted to verify the effectiveness of the IRSMC DPC strategy. The results show that this strategy ensures satisfactory performance of the system over a wide range of operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, a method for suppressing the low-frequency portion of dc-link ripple inevitably present in power conversion systems with reduced capacitance is proposed. The discussed active capacitance reduction circuitry (consisting of a feedback-controlled shunt-connected bidirectional buck-boost converter, terminated by a small auxiliary capacitance) directly regulates the dc-link voltage, utilizing a dual-loop control structure with parallel-connected multiresonant-bank-enhanced voltage loop stabilizing controller to achieve nearly constant, low-frequency-ripple-free steady-state dc-link voltage. Consequently, the proposed active capacitance reduction system may be perceived as a virtual infinite capacitor from the dc link point of view. The suggested circuitry is successfully applied to a single-phase commercial power factor correction front end in a nearly plug-and-play fashion. The control algorithm effectiveness is fully supported by simulations and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control strategy to deal efficiently with the recurrent frequency and amplitude adjustments that occur in standalone microgrid application. These frequent variations are commonly introduced by the droop based controllers in order to accurately regulate the power sharing among the parallel connected distributed generators. In this way, a double current and voltage control structure based on adaptive proportional plus multi resonant controllers is designed to address the aforementioned challenges. The proposed adaptive control technique allows maintaining high performance voltage reference tracking with a reduced rate of harmonic distortion in spite of load transients and under significant operating frequency deviation. The designed control structure is then expanded to parallel-distributed generation units through a modified droop based power-sharing controller. Experimental results are presented to show the feasibility of the proposed adaptive control scheme and its effectiveness to cope with large frequency variations. [ABSTRACT FROM AUTHOR]

High Altitude Wind Power (HAWP) generating system provides clean energy at low cost and high capacity factor due to reduced size of the turbine and high speed streamlined wind at high altitude. An air-borne wind turbine (AWT) at high altitude extracts kinetic energy from wind using buoyancy provided by the blimp/aerostat. The generated electrical power is then transmitted to the ground based station (without any power conditioning) using the transmission lines (tether). The power conversion system (PCS) for harnessing HAWP is proposed in this paper. The proposed PCS consists of a three-level neutral point clamped (NPC) rectifier, a three-level NPC DC–DC converter followed by a two-level inverter. Modelling, design and control of the PCS are presented and discussed. The PCS provides generation side maximum power-point tracking (MPPT) using sensorless optimal torque control technique. The DC–DC converter provides electrical isolation as well as voltage step-down functions. A modified proportional resonant (PR) control which can selectively eliminate lower order current harmonics of the grid-connected inverter is also presented. The proposed control scheme of the PCS is evaluated through simulation studies using software programs like PSIM and MATLAB. A scaled-down 1 kW laboratory prototype of the complete PCS is designed, built and tested. The experimental test results obtained validate the proposed control scheme for efficient power generation from high altitude wind and interface to the grid/load. [ABSTRACT FROM AUTHOR]

Numerous dynamic atomic force micros- copy (AFM) methods have appeared in recent years, which make use of the excitation and detection of higher order eigenmodes of the microcantilever. The ability to control these modes and their responses to excitation is believed to be the key to unraveling the true potential of these methods. In this paper, we highlight a multimode $Q$ control method that exhibits remarkable damping performance and stability robustness. The experimental results obtained in ambient conditions demonstrate improved imaging stability by damping nondriven resonant modes when scanning is performed at a higher eigenmode of the cantilever. Higher scan speeds are shown to result from a decrease in transient response time. [ABSTRACT FROM PUBLISHER]

The vector control algorithm based on vector space decomposition (VSD) transformation method has a more flexible control freedom, which can control the fundamental and harmonic subspace separately. To this end, a current vector decoupling control algorithm for six-phase permanent magnet synchronous motor (PMSM) is designed. Using the proposed synchronous rotating coordinate transformation matrix, the fundamental and harmonic components in d− q subspace are changed into direct current (DC) component, only using the traditional proportional integral (PI) controller can meet the non-static difference adjustment, and the controller parameter design method is given by employing internal model principle. In addition, in order to remove the 5th and 7th harmonic components of stator current, the current PI controller parallel with resonant controller is employed in x− y subspace to realize the specific harmonic component compensation. Simulation results verify the effectiveness of current decoupling vector controller. [ABSTRACT FROM AUTHOR]

A significant number of power apparatus, before being commercialized or during maintenance, are submitted to laboratory tests where real operation conditions are emulated. These tests generally demand high energy consumption which increases the maintenance costs and the overall equipment investment. This paper proposes a platform to test power transformers with return of energy (closed loop) to the system, reducing the power consumption to the inherent equipment losses. Besides the low energy consumption, the proposed system permits flexible tests and operation with variable power factor. The transformer under test can be submitted to different load profiles, including harmonics injection, which is not generally addressed in the traditional procedures. The control structure and constructive characteristics of a 75-kVA test bench are presented and the methodology is validated by testing a 50-kVA distribution transformer. The experimental results are discussed, and the overall system efficiency is demonstrated. [ABSTRACT FROM AUTHOR]

This paper investigates a combined resonant–repetitive (RR) control structure for a three-phase four-leg dc/ac converter power supply. The RR control configuration is composed by a resonant controller tuned at the system fundamental frequency working in conjunction with a plug-in-type repetitive controller. The resonant part of the control scheme is used to assure prompt tracking of the inverter output voltage and to achieve as fast as possible system response to load variations; to this purpose, it is tuned at the fundamental frequency. At the same time, the resonant controller is able to stabilize the system without the necessity of any further additional controller; the repetitive part of the scheme is implemented for the fine regulation at the system harmonic frequencies. The proposed control configuration is used to regulate the power supply output voltage, providing very good tracking of the output voltage reference even in the presence of a nonlinear load. Experimental validation from a 40-kVA converter prototype is presented to validate the operation of the proposed converter and control. [ABSTRACT FROM PUBLISHER]

To reduce the undesired 5th and 7th stator harmonic current in the six-phase permanent magnet synchronous motor (PMSM), an improved vector control algorithm was proposed based on vector space decomposition (VSD) transformation method, which can control the fundamental and harmonic subspace separately. To improve the traditional VSD technology, a novel synchronous rotating coordinate transformation matrix was presented in this paper, and only using the traditional PI controller in d – q subspace can meet the non-static difference adjustment, the controller parameter design method is given by employing internal model principle. Moreover, the current PI controller parallel with resonant controller is employed in x – y subspace to realize the specific 5th and 7th harmonic component compensation. In addition, a new six-phase SVPWM algorithm based on VSD transformation theory is also proposed. Simulation and experimental results verify the effectiveness of current decoupling vector controller. [ABSTRACT FROM AUTHOR]