Multiple Resonant Controllers Research Articles

Harmonic vibration suppression of MSCSG Based on an Improved Multiple Resonant Controller

Harmonic vibration suppression of MSCSG Based on an Improved Multiple Resonant Controller

Harmonic characteristics and control strategies of grid-connected photovoltaic inverters under weak grid conditions

To investigate the harmonic characteristics of a photovoltaic (PV) system connected to the weak grid, a passive impedance network is constructed using the impedance model of a PV inverter in the positive and negative sequence coordinate system. By analyzing the series resonance of the impedance network, the amplification coefficient of the harmonic voltage at the point of common coupling (PCC) is obtained. In addition, the effects of different PV inverter parameters, different reactive power compensation capacities, and different lengths of distributed transmission lines on the harmonic amplification are analyzed in detail. To solve the problem that the output harmonics exceed the standard under the background harmonic condition of the weak grid, a harmonic mitigation control strategy is implemented. This strategy is designed based on multiple resonant current controllers and active damping feedback to improve the ability of the PV inverter to suppress harmonics under the grid background harmonic conditions. The effectiveness of the harmonic mitigation control strategy is demonstrated by the simulation example of the inverter connected to the grid with symmetric and asymmetric background harmonics, respectively.

Analysis and Design of Multiple Resonant Current Control for Grid-Connected Converters

Including “generalized integrators” for sinusoidal signals, multiple resonant control (MRSC) scheme which can accurately compensate selected sinusoidal signals, is widely used as a high-performance current control method for grid-connected converters. In this article, the plug-in digital plug-in MRSC scheme is proposed to provide a general framework for housing various MRSC schemes, which plugs the MRSC controller into a stable feedback control loop. It can take advantages of both controllers—the feedback controller provides fast response and good robustness, and the MRSC controller offers accurate compensation of the periodic signals. More critically, based on a new type of sinusoidal signal model, the sufficient stability criteria and the gain tuning rules are developed to offer a simple universal approach to the design of the digital plug-in MRSC schemes. An application case study on the digital plug-in MRSC of a 5-kVA three-phase four-wire grid-connected inverter with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> filter is provided. Experimental results demonstrated that the proposed MRSC scheme can force the inverter to produce high-quality currents with high accuracy, fast transient response, and good robustness.

Mixed H2/H∞ Optimal Voltage Control Design for Smart Transformer Low-Voltage Inverter

The smart transformer has been widely applied for the integration of renewables and loads. For the smart transformer application, the voltage control of low-voltage inverter is important for feeding the load. In this paper, a multi-objective optimization control design approach which comprehensively considers all aspects of indexes, such as linear quadratic (LQ) index, H∞ norm, and closed-loop poles placement, is proposed based on the linear matrix inequality (LMI) solution. The proposed approach is able to alleviate the weight of the designer from the tedious design process of the multiple resonant controllers and the selection of the weighting matrix for the LQ control. Besides that, some excellent performances such as fast recovering time, low total harmonic distortion (THD) and high robustness are achieved by the proposed approach. The THD are 0.5% and 1.7% for linear and non-linear loads, respectively. The voltage drop for linear load step is reduced to 10 V. The proposed approach is applied to a 5 kVA three-phase inverter to yield an optimal control law. Results from the simulation and experiment presented herein will illustrate and validate the proposed approach.

Passive control of multiple structural resonances with piezoelectric vibration absorbers

A novel sequential tuning procedure for passive piezoelectric shunts targeting multiple structural modes is proposed in this work. The control authority on each targeted mode can be quantitatively chosen ab initio and is shown to be limited by passivity requirements, which highlights the fundamental limitations of multimodal piezoelectric shunts. Based on effective characteristics of the piezoelectric system around resonance, electrical damping ratios and resonance frequencies are derived using well-established single-mode formulae from the literature, thereby fully specifying the characteristics of the shunt impedance. The proposed approach is numerically verified and experimentally validated on piezoelectric beams by emulating the shunt with a digital vibration absorber.

A Novel Design of PR Controller With Antiwindup Scheme for Single-Phase Interconnected PV Systems

This article presents the design methodology of an alternative approach for implementing proportional-resonant (PR) controller for single-phase grid-tied inverter. The developed PR controller is designed to regulate the grid current with the aim of controlling either the dc-link voltage or the active/reactive power injected into the grid. The control design is based on combining a state feedback controller with a disturbance observer. It turns out that the composite controller can be expressed as a PR controller plus an antiwindup scheme. The latter is required by the resonant portion of the PR controller to attenuate the effect of the control input saturation during transients. On the other hand, when the voltage harmonics are taken into account in the observer design, the composite controller reduces to multiple resonant controllers with an antiwindup scheme. The performance of the existing PR controller was investigated under control saturation to highlight the poor transient performances associated with modulating signal limitation. Experimental tests have been conducted to verify the the performance of the proposed controller. The obtained results demonstrated good transient performances compared with the existing PR controller, particularly during control saturation. Furthermore, performance results under voltage harmonics showed that the proposed controller can achieve accurate control of the current with low total harmonic distortion values.

Parameter co-design of active damping loop and grid current controller for a 3-phase LCL-filtered grid-connected inverter

Under non-ideal grid conditions, especially the harmonic grid condition, the proportional resonant controller with multiple harmonic resonant controllers (HR-PR controller) is recommended to provide high quality grid currents for the 3-phase LCL-filtered grid-connected inverter. Besides, in order to solve the resonance problem, the active damping loop with the grid-side currents feedback only is preferred. However, parameters of the HR-PR controller and the active damping loop both affect the performance of LCL filter resonance suppression and stability of the inverter, which is analyzed in this paper. Moreover, the stability constraint and the resonance suppression constraint is derived to maintain the good ability of LCL filter resonance suppression and satisfy the stability requirements of the inverter. Considering the wide control bandwidth for the HR-PR controller, a co-design method of the active damping loop and HR-PR controller is proposed in this paper. By introducing the Lagrange multiplier method, the proposed co-design method obtains the optimized parameters for the active damping loop and grid currents controller in z-domain appropriately. A prototype of 3-phase LCL-filtered three-level neutral point clamped grid-connected inverter is established to validate the proposed method.

Current Control of Grid-Tied LCL-VSI With a Sliding Mode Controller in a Multiloop Approach

Despite several studies and approaches, the design of current controllers for grid-connected converters via LCL filters is still a challenging task. This is mainly due to the parametric uncertainties and the grid background voltage distortions to which the system is submitted. In order to overcome these inherent system challenges, this paper proposes a multiloop control framework that simplifies the system dynamics of the overall circuit by splitting it in two equivalent sub-circuits. An inner loop is implemented as a fast sliding mode controller that controls the filter capacitor voltage in a fast and robust way. As a result, the plant, viewed by the outer loop, yields a voltage-controlled voltage source connected to the grid through an L filter. Thus, multiple resonant controllers are included in the state-space representation of this simplified system, allowing the design of a state-feedback controller in the outer loop for asymptotic tracking of the grid current with disturbance rejection of the grid background voltage. Here, a discrete linear quadratic regulator algorithm is used for designing the state-feedback gains. A simple design procedure is presented, as well as simulations and experimental results, to show the good performance of the proposed control scheme even under significant uncertainties and disturbances of the system.

Affine discretization methods for the digital resonant control of uninterruptible power supplies

This paper addresses the discrete-time design and performance evaluation of finite-gain multiple resonant controllers for uninterruptible power supplies – UPS. Two discretization methods that preserve the affinity with respect to time-varying parameters are considered to obtain the discrete-time UPS uncertain model. Based on a state-feedback formulation for the proposed controller, a systematic approach for the robust design of controller gains is derived by the solution of a convex optimization problem subject to linear matrix inequality constraints. Simulation and experimental results in a 3.5 kVA inverter are obtained to compare the effects of distinct sampling frequencies and plant discretization methods with respect to the IEC 62040-3 performance parameters.

A Design Methodology of Multiresonant Controllers for High Performance 400 Hz Ground Power Units

In aerospace applications, a ground power unit has to provide balanced and sinusoidal $\text{400}\,\text{Hz}$ phase-to-neutral voltages to unbalanced and nonlinear single-phase loads. Compensation of high-order harmonics is complex, as the ratio between the sampling frequency and compensated harmonics can be very small. Thus, multiple superimposed resonant controllers or proportional-integral (PI) nested controllers in multiple $dq$ frames are not good alternatives. The first approach cannot ensure stability, while the second cannot track the sinusoidal zero-sequence components typically present in unbalanced systems, and unattainably high bandwidth at the inner current control loop is typically required. In this paper, a simple methodology for designing a single-loop, multiple resonant controller for simultaneous mitigation of several high-order harmonics, ensuring stability, is presented. Experimental results, based on a 6 kW four-leg neutral point clamped converter, validate the proposed controller design, showing excellent steady-state and transient performance.

Hardware-in-the-Loop for Wind Energy Conversion with Resonant Current Control and Active Damping

In this paper, the design of current control system based on multiple resonant controllers with active damping control strategy for wind energy conversion system in Back-To-Back configuration with LCL filter is presented. Due to its ability to perform control and compensation of the injected currents into the network, the proposed system is a resonant current control (PR) and harmonic compensators (HC) of fifth and seventh order that allows the injection of currents with low harmonic distortion to the electrical network. The high frequency harmonics generated by the converter are damped by LCL filter. As a solution to the effects of the resonance frequency of the LCL filter, the active damping strategy is implemented. This improve the quality of current signal significantly, obtaining a THDi= 3.56\% and percentage level of each current harmonic lower than 2\%. The proposed control interacts in real time with the wind energy conversion system through the Hardware-in-the-Loop technique carried out in the Triphase PM5F60R, located in the microgrid laboratory of the University of Chile.

Limitations of Harmonics Control in Power Converters

In this paper, we analyze the constraints of harmonics control in power electronic systems. Based on an equivalent circuit of a typical power converter application and its parameters, we have derived an analytical expression for calculating the maximal amplitude of controlled harmonic current. This expression has been successfully verified on an experimental setup, designed around a single-phase grid-connected bidirectional inverter. The pulse width modulated (PWM) driven inverter has been controlled by multiple resonant controllers, each of them providing individual control of a selected harmonic current. By using the derived expression and taking into account the parameters of converter application, power electronics designers could quickly determine the limitations of harmonics control.

Multirate Resonant Controllers for Grid-Connected Inverters With Harmonic Compensation Function

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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -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.

Performance Improvement of Bearingless Multisector PMSM With Optimal Robust Position Control

Bearingless machines are relatively new devices that consent to suspend and spin the rotor at the same time. They commonly rely on two independent sets of three-phase windings to achieve a decoupled torque and suspension force control. Instead, the winding structure of the proposed multisector permanent magnet (MSPM) bearingless machine permits to combine the force and torque generation in the same three-phase winding. In this paper, the theoretical principles for the torque and suspension force generation are described and a reference current calculation strategy is provided. Then, a robust optimal position controller is synthesized. A multiple resonant controller is then integrated in the control scheme in order to suppress the position oscillations due to different periodic force disturbances and enhance the levitation performance. The linear quadratic regulator combined with the linear matrix inequality theory has been used to obtain the optimal controller gains that guarantee a good system robustness. Simulation and experimental results will be presented to validate the proposed position controller with a prototype bearingless MSPM machine.

Dual-Loop-Based Current Controller for Transformerless Grid-Tied Converters with Improved Disturbance Attenuation against Voltage Measurement Errors

To eliminate current harmonics and to obtain enhanced dynamic behaviors, the voltage feedforward scheme is normally adopted in the control process of transformerless grid-tied converters. However, voltage measurement errors caused by parameter variation of sampling resistance and zero-voltage drift in analog devices will result in DC current injection and distorted grid currents in grid-tied systems. Conventional compensation strategies based on plug-in repetitive controllers and multiple resonant controllers are considered to be effective solutions to solve this problem. Even though undesired components in grid currents can be partially mitigated with these conventional compensation schemes adopted, degraded reference-tracking process with oscillations and slow dynamics are inevitably caused by the controller coupling. To obtain decoupling between reference tracking and disturbance rejection, this paper proposes a dual-loop controller to achieve current regulation and to suppress the disturbances caused by voltage measurement errors. With the proposed dual-loop controller adopted, DC current injection and distortion of grid currents can be effectively attenuated while excellent transient performance with negligible overshoot and fast step response can be simultaneously guaranteed. Frequency-domain analysis and experimental validations are both conducted to verify the effectiveness of the proposed strategy.

Control of Multiple Fano Resonances Based on a Subwavelength MIM Coupled Cavities System

In this paper, we investigate and analyze numerically and theoretically a coupled plasmonic resonant system by using finite-difference time-domain (FDTD) method and multimode interference coupled-mode theory (MICMT), respectively. First, by employing an end-coupled cavity associated with two side-coupled cavities, three ultra-sharp and asymmetrical Fano resonant peaks are observed in the transmission spectrum. High refractive index sensitivities and high figure of merits are achieved for all the peaks. In the interest of highly integrated optical devices, up to seven Fano peaks with asymmetrical line shapes are achieved when the composite structure is successfully extended by two additional cavities, whereas most of the reported results are about 1-4 Fano resonances in a single structure. Preferred performances are also obtained for this chip-scale structure. This proposed structure may have great potential applications for on-chip optical sensing and optical communication in highly integrated photonic circuits.

Multiple resonant controllers strategy to achieve fault ride‐through and high performance output voltage in UPS applications

A control strategy to achieve fault ride-through capability and to provide high performance of the output voltage of a single-phase uninterruptible power supply (UPS) inverter is proposed in this study. This strategy consists in controlling the voltage and current waveforms measured at the inverter output filter, with an inner current control loop and an outer voltage control loop, using a plug-in structure based on multiple resonant stages in addition with proportional controllers. In order to achieve stability from no load to short-circuit conditions, the implementation of the multiple resonant controllers includes a compensation of the system phase lag. Moreover, it presents a comparative analysis between two controller structures, the proposed plug-in and the classical proportional + resonant. From this analysis, it can be concluded that the plug-in structure presents improved characteristics of closed-loop output impedance and output voltage dynamic response during fault ride-through events. A controller design methodology to achieve robustness to parametric uncertainties and UPS standard compliance, is detailed. Experimental results from a single-phase 2 kVA inverter prototype are presented to validate the feasibility of the proposal.

Research on Active Control Strategy of Grid Connected Harmonic Current Based on Hierarchical Control for Microgrid

The micro grid connected in parallel with the traditional droop controlled voltage source inverter is easily affected by the disturbance of the harmonic component of the grid and the dot voltage when the equivalent output impedance is smaller. The total harmonic distortion rate of the grid connected current is raised. An active lifting control strategy for grid connected current power quality based on layered control is proposed. First, the Park transform is used to transform the error voltage between the node and the micro grid AC bus to the rotating coordinate system, and the error voltage compensation loop is added to the two layer control of the original microgrid, and the parallel connection in the compensation loop is used. The multiple resonant controller calculates the error voltage, obtains the harmonic voltage compensation of the underlying voltage source inverter, and uses the proportional integral and resonant hybrid controller based on the rotating coordinate system in the voltage and current inner loop of the inverter to improve the tracking ability of the inverter to the harmonic voltage compensation, and then reduce the micro grid. The harmonic voltage difference between the AC bus and the parallel node reduces the harmonic current injected into the grid by the microgrid. The analysis shows that the control strategy described in this paper can not only reduce the steady-state harmonic current injected into the power grid, but also reduce the harmonic current impact of the grid to the micro grid because of the closing of the grid switch. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiments.

Robust Design of LCL Filters for Single-Current-Loop-Controlled Grid-Connected Power Converters With Unit PCC Voltage Feedforward

The point of common coupling (PCC) voltage feedforward control is widely employed for LCL-type grid-connected converters to prevent large inrush current during startup, reduce steady-state tracking error, and suppress disturbances of grid voltage. Generally, this feedforward loop is ignored in the system modeling and stability analysis for simplicity. However, the grid impedance would be introduced to the control system through the feedforward loop under practical power grids, leading to a different current loop model from the original one, then conventional LCL filter design for single-current-loop control may be inappropriate. In this paper, the detailed modeling of current control loop with unit PCC voltage feedforward is presented. Based on the established model, it is found that unstable open-loop poles may appear under grid impedance variation, which thus may cause system instability. Therefore, the robust design regions of LCL filters against grid impedance variation are proposed for single-current-loop control schemes. Moreover, another interesting finding is that the feedforward control can help maintain a high current control bandwidth under grid impedance variation. This feature is highly desirable if multiple resonant controllers are employed for harmonic compensation. Experimental results are finally presented to verify the theoretical analysis and robust design presented in this paper.

High-Precision Speed Control Based on Multiple Phase-Shift Resonant Controllers for Gimbal System in MSCMG

The high precision speed control of gimbal servo system in magnetically suspended control moment gyro (MSCMG) suffers from periodic torque disturbances, which lead to periodic fluctuations in speed control. This paper proposes a novel multiple phase-shift resonant controller (MPRC) for a gimbal servo system to suppress the periodic torque ripples whose frequencies vary with the operational speed of the gimbal servo motor and high-speed motor. First, the periodic torque ripples caused by cogging torque, flux harmonics and the dynamic unbalance of the high speed rotor are analyzed. Second, the principle and structure of MPRC parallel with proportional integral (PI) controllers are discussed. The design and stability analysis of the proposed MPRC plus PI control scheme are given both for the current loop and speed loop. The closed-loop stability is ensured by adjusting the phase in the entire operational speed range. Finally, the effectiveness of the proposed control method is verified through simulation and experimental results.