Multi-resonant Controller Research Articles

Design and Control of Single-Phase Double-Stage PV-MPPT System

In the double-stage Photovoltaic-Maximum Power Point Tracking (PV-MPPT) systems, the performance of each stage and the MPPT algorithm may affect the system performance. This study gives the design and control of a single-phase double-stage PV-MPPT system with a cascade controller. For the DC-link voltage control, a classical PI controller is employed. However, double-line frequency harmonic emerges inherently in the DC-link voltage. This voltage harmonic causes a third harmonic in the injected grid current. Therefore, a proportional multi-resonant controller is used in the inner current loop controller to control the grid current and suppress the third harmonic. The designed system's steady-state and dynamic performance are tested under different PV power and sudden power changes. The simulation results show that the injected grid current is in phase with the grid voltage and has a low THD value. Also, the DC-link voltage is stable under even sudden power changes. The results prove the effectiveness of the designed system.

An Improved digital multi-resonant controller for 3 [formula omitted] grid-tied and standalone PV system under balanced and unbalanced conditions

With the exponential penetration of Photovoltaic (PV) plants into the power grid, advanced current controllers should be employed in grid-tied power converters in order to efficiently inject high quality current synchronized with the grid voltage. This research presents the modeling and design of a digital multi-resonant controller to feed-in high quality current. The novelty lies in designing the control in a superior manner to conventional techniques. As an outcome, practical engineers discover an easy, fast, robust, and accurate control method. The proposed 5-kVA PV system can inject active and reactive power effectively while staying resilient to imbalance scenarios. Synchronization is accomplished via a synchronous reference frame (SRF) based phase locked loop (PLL) that performs effectively even with distorted and nonideal grids. The practicality and efficacy of the developed controller is verified both in simulation (PSIM and code composer studio) and Hardware in Loop (HIL) via Typhoon 402 and TMS32F28335 experiments. The devised controller is evaluated in both grid-connected and standalone modes under a wide range of disturbances, distortions, and non-ideal conditions. The simulation and HIL results validate the robustness, fastness, resilience, and effectiveness of the proposed controller compared with a well-tuned conventional proportional resonant (PR) controller.

An improved IPT-PLL technology for single-phase grid-connected inverters in complex power grid conditions

Aiming at the common problems of frequency variations and harmonics in complex power grids, an improved inverse Park transform phase locked loop (IPT-PLL) technology for single-phase converters suitable for micro grid systems is proposed. Firstly, in the phase detection of PLL, the α component of Park transformation is selected as the reference voltage, and its orthogonal component is constructed using a 1/4 fundamental period delay method. Secondly, Lagrange interpolation polynomials are introduced to approximate fractional delay to solve the problem of delay calculation errors caused by frequency changes. Thirdly, in order to compensate for the poor ability of traditional proportional integral (PI) regulators, multi resonant controllers are superimposed to suppress low order harmonic disturbances. Finally, the design method and system performance of the PI regulator and each resonant controller are analyzed theoretically. The experimental results show that the proposed improved IPT-PLL method has strong adaptability to complex power grids. It can significantly improve the tracking performance of power grid frequency, suppress the interference of low order harmonics and DC bias. And it has good dynamic and static performance.

Smart Nonlinear Energy Feedback Power Electronic Load to Simulate Power Quality Problems

This paper proposes a design approach for an energy feedback power electronic load (PEL) based on back-to-back voltage source PWM converters. It can simulate not only constant linear loads but also a class of nonlinear loads to simulate power quality problems. The rectifier side and the inverter side are decoupled in control by using a DC capacitor. The rectifier side is responsible for tracking designed current commands to achieve the designed load characteristics, and based on the characteristics of the current commands, a multi-resonant controller plus state feedback controller was designed by using the internal model principle. The inverter side employs an LCL filter with active damping to control the phase of the grid-connected current, enabling energy to feed back to the grid. A simulation model of this PEL is established in Simulink software, and the simulation results verify the effectiveness of the proposed control strategy.

Multi-resonant Controller Design for a PV-Fed Multifunctional Grid-Connected Inverter in Presence of Unbalanced and Nonlinear Load

The use of Active Power Filters (APFs) in future power grids with high penetration of nonlinear loads is unavoidable. Voltage Source Inverters (VSIs) interfacing Photovoltaic (PV) generator could play the APF role in addition to power supply. In this paper, the control of a PV-fed multifunctional grid-connected three-phase VSI is addressed with nonlinear and unbalanced load. The control objective is threefold. The first one is to deliver the maximum available power from the PV source to the grid satisfying power quality standards. The second one is the Voltage Balancing Control for DC-link capacitors to guarantee correct operation of the VSI. The last one is shunt APF control to compensate for nonlinear and unbalanced load harmonics, reactive power, and unbalanced sequences. A quasi-Proportional-Resonant (PR) controller with harmonic compensators is proposed for the current control loop. The quasi-PR controller parameters are determined through optimization algorithms such as Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and a combination of both PSO and GA. The aim of the objective function is to improve static and dynamic behavior. The different gains at the fundamental resonant frequency and the selected odd harmonics are obtained for the proposed quasi-PR controller. The dynamic characteristics of the optimized quasi-PR controllers show superiority against conventional ones in terms of gain margin, phase margin, overshoot, and robustness. With the proposed control scheme, the harmonics, reactive power, and unbalanced sequences are appropriately compensated. The performance of the PV-fed VSI shunt APF under irradiance change, load change, and distorted grid voltage conditions is validated through numerical simulations performed on hbox {PSIM}^{copyright } software. The results show that the grid currents Total Harmonic Distortion for irradiance change case study are 4.57%, 4.57%, and 3.22% in phase a, b, and c with the proposed control method, while they are 9.25%, 5.65%, and 10.12% with conventional instantaneous p-q theory.

A New Approach to Enhance the Operation of M-UPQC Proportional-Integral Multiresonant Controller Based on the Optimization Methods for a Stand-Alone AC Microgrid

This article aims to improve the power quality components of the AC microgrid (ACMG). The proposed module for this article is a modified-unified power quality conditioner (M-UPQC). The M-UPQC controller performs on principles of current and voltage source inverters and the resonant component of the system. Here, the research innovation consists of two sections: first, the modification of the desired module controller setting according to the power quality nature received from the grid to find the best parameters for resetting the M-UPQC controller; second, adjusting the proportional-integral multiresonant (PI-MR) control parameters of M-UPQC by the black hole optimization (BHO) and particle swarm optimization (PSO) techniques. In the following, the proposed procedure will be a programmed multiobjective technique. The designed multiobjective functions will be optimized by the BHO and PSO methods to adjust PI-MR controller parameters to reduce the system harmonic perturbations. The simulation results show the improvement of the ACMG operation by considering the proposed technique. To confirm the results obtained from the case study simulation platform, the experimental results of the harmonic components are presented in the results section.

Implementation and performance comparison of harmonic mitigation schemes for three-phase grid-connected voltage-source converter under grid voltage distortion: HiL and experimental validation

This paper presents an implementation methodology for a current harmonic compensation technique of three-phase grid-connected voltage-source converter (VSC), which was applied under the grid voltage distortion and frequency variation. The proportional–integral plus multi-resonant controllers (PIMR) were used to mitigate the high-order harmonic current. The harmonic compensators were used in the synchronous reference frame at harmonic orders 6th and 12th for suppression of the grid voltage harmonic orders 5th, 7th, 11th, and 13th with a total harmonic distortion of 4.69%. The PIMR controller was transformed to the discrete-time domain and implemented on a TMS320F28379D digital signal processor. The PIMR controller was compared with the conventional multiple synchronous reference frame (PIMSR) controller. The two control schemes were validated with a hardware-in-the-loop (HiL) and with a 5 kW three-phase LCL-filtered grid-connected VSC. The PIMR and PIMSR controllers exhibited excellent harmonic rejection on the grid current with a total harmonic distortion close to 1%, which complied with the IEEE 1547 standard. The grid current can track the reference command with a fast dynamic response. Moreover, the PIMR controller consumed a computational time of 1.625μs, 35% of the PIMSR controller.

A harmonic suppression strategy for grid-connected inverters based on quadrature sinewave extractor

Grid-connected inverters need to reduce current harmonics as much as possible. After introducing the input signal’s fundamental and main harmonic quadrature components, a discrete state model is created, and the discrete observer design method is used to propose a harmonic extraction algorithm called quadrature sinewave extractor (QSE). The QSE is a stable recursive operator with the advantages of no phase displacement and the ability to eliminate mutual influence between harmonic components. Compared to the widely used proportional multi-resonant controller, QSE can reduce current harmonics and improve system stable performance by using it in the current control of grid-connected inverters. Finally, comparative experiments on a three-phase grid-connected inverter are used to verify the proposed method’s effectiveness.

Hybrid Active Power Filter for Power Quality Improvement

A Deadbeat current controller for an LC-coupling hybrid active power filter is proposed, which can track with the reference compensation current with low steady- state error and fast dynamic response. Moreover, it can lead Hybrid Active power Filter to be operating at a fixed switching frequency with low output current ripples, thus reducing the size of the filtering circuit. The stability issue and parameter design of the proposed deadbeat current controller are analyzed and discussed. Finally, the compensating performance of the deadbeat current controller for the Hybrid Active Power Filter (LC-HAPF) is verified by simulation compared with the conventional hysteresis bandwidth modulation control, the proportional-integral (PI) control, and the proportional multi-resonant control for the LC-HAPF, which shows its effectiveness and superior compensating performances.

Modeling, Simulation and Development of Grid-Connected Voltage Source Converter with Selective Harmonic Mitigation: HiL and Experimental Validations

This paper elaborates on a development technique for the grid-connected voltage source converter (VSC). We propose a simulation technique in the MATLAB/Simulink environment that emulates the operation of the discrete-time controlled grid-connected VSC. The switched-circuit modeling approach is used for simulation of the power stage in the continuous-time domain with the physical unit scale. The discrete-time control algorithm is implemented in an interpreted MATLAB function in the per-unit scale, which synchronizes with the switching period. Such a control algorithm is easily translated into the C language for programing of the 32-bit C2000 DSP controller with the same regulators’ parameters. The proposed platform was validated with a hardware-in-the-loop real-time simulator and with a 5-kVA 3-phase LCL-filtered grid-connected VSC. The discrete-time control scheme was implemented in the synchronous reference frame control with proportional-integral with multi-resonant controllers at harmonic orders 6th and 12th for suppression of the grid voltage harmonic orders 5th, 7th, 11th, and 13th. The experimental results closely agreed with the simulation results. The experimental grid currents complied with the IEEE 1547 standard thanks to the multi-resonant controllers. The proposed platform provides a smooth transition from implementation to a near-commercial prototype with a low investment cost in simulation and rapid prototyping tools. A MATLAB/Simulink VSC model is provided as an attachment of this paper.

Tuning of state-feedback multi-resonant controllers based on LQR using differential evolution metaheuristic

This paper proposes a generic methodology for tuning state-feedback multi-resonant (SF-MR) controllers in power electronics applications involving L, LC, and LCL filters. The tuning of the controllers is performed using differential evolution metaheuristic in conjunction with the well-known linear-quadratic regulator (LQR) approach. This optimization algorithm avoids the empirical trial-and-error method for adjusting the weighting values of Q and R matrices while minimizing the cost function based on a weighted sum of the total harmonic distortion of the controlled variables, control loop errors, and control signals saturation. Thus, an adequate approach to adjust LQR-SF-MR controllers is achieved, proving useful for controlling active power filters (APF) since non-sinusoidal control references are involved. Furthermore, the proposed tuning method is appropriate for controlling voltage source inverters (VSI) following sinusoidal references and feeding non-linear loads since the high rejection of harmonic disturbances is reached. The effectiveness of the proposed design methodology for controllers' tuning is tested in a current-controlled 3-phase 4-wire (3P4W) shunt-APF, grid-connected through both L and LCL filters, as well as in a voltage-controlled 3P4W VSI connected to non-linear loads with LC filters. The control performances of the systems are extensively evaluated through experimental results.

WEC Array Optimization with Multi-Resonance and Phase Control of Electrical Power Take-Off

This new research provides transformative marine energy technology to effectively power the blue economy. Harmonizing the energy capture and power from Wave Energy Converter (WEC) arrays require innovative designs for the buoy, electric machines, energy storage systems (ESS), and coordinated onshore electric power grid (EPG) integration. This paper introduces two innovative elements that are co-designed to extract the maximum power from; i) individual WEC buoys with a multi-resonance controller design and ii) synchronized with power packet network phase control through the physical placement of the WEC arrays reducing ESS requirements. MATLAB/Simulink models were created for the WEC array dynamics and control systems with Bretschneider irregular wave spectrum as inputs. The numerical simulation results show that for ideal physical WEC buoy array phasing of 60 degrees the ESS peak power and energy capacity requirements are minimized while the multi-resonant controllers optimize EPG power output for each WEC buoy.

Analysis and Suppression of Voltage Harmonic Distortions of the Single-Phase High Frequency Link Matrix-Type DC–AC Converter

The single-phase high frequency link (HFL) matrix-type DC-AC converter has been widely explored due to its high efficiency, light weight, and high power density, which offers galvanic isolation power conversion without bulky dc link capacitors and soft-switching operation. Different from traditional two-level DC-AC converters, the single-phase HFL matrix-type DC-AC converter has no double-line frequency ripple voltage on the DC side, but the ripple appears on the clamp capacitor, which has not yet been investigated in detail so far. In this paper, the mechanism of the double-line frequency ripple voltage of the clamp capacitor in the single-phase HFL matrix-type DC-AC converter is comprehensively explored, and a mathematical model of the HFL matrix-type DC-AC converter is established. To suppress the effect of the double-line frequency ripple voltage on the power quality and guarantee the good power quality of the AC side, a multi-resonant (MPR) controller is applied to reduce voltage harmonic distortions. A 20-kHz HFL matrix-type DC-AC converter prototype is built. Experimental results have verified the effectiveness of the analysis and applied control scheme.

Robust Tuning of Multiresonant Current Controllers for Grid-Tied Converters and Erroneous Use of the Naslin Polynomial Method

The majority of the paper is devoted to debunking flawed methods proposed in the literature within the context of multiresonant control systems for grid-connected converters and then a novel approach is proposed. Several flawed approaches to grid tied power electronic converters (rectifiers and shunt active power filters) are discussed to initiate a critical discussion regarding some tuning methods reported in the topical literature. In this paper we analytically show that some of them are even erroneous from the control theory point of view or are based on mathematically erroneous derivations. That is especially prevalent for papers in which the Naslin polynomial method is employed to tune proportional-multiresonant controllers. Some authors recognize that the resulting control systems are not robust, i.e. not practical, and use obtained gains only as a starting point for further tuning using the trial and error method or evolutionary global optimization. Robustness of such systems is often not guaranteed and if it occurs at all, it is by chance or thanks to a combination of luck and expert knowledge of the engineer (not by deliberate design). Therefore, the absence of such a guarantee motivates the search for better ways to tune such controllers. As a result, a practical robust controller tuning method for multiresonant grid current controllers is proposed and verified experimentally. We are convinced that one of the solutions can be based on the disk margin stability analysis and a global search algorithm. The required robustness is expressed as stability margins. The design procedure is very user-friendly and the disk size is the key design parameter to be selected by an engineer. The practicality of the tuning method is demonstrated empirically in a 10 kVA physical grid-tied converter.

An Improved Hierarchical Control Structure for Robust Microgrid Operation and Seamless Mode Transfer under Linear and Nonlinear Loads conditions

This paper proposes the improved hierarchical- based control of Microgrid based on proportional and multi-resonance controllers to compensate for harmonic distortion of nonlinear loads. Moreover, the probable transition of MG, especially from grid-connected to unplanned islanding and unintentional MG resources outage are studied. In current and voltage controllers of three-phase VSIs which are located in the inner level, the proportional and multi-resonant controllers are implemented. To attain proper decoupled (P-Q) power-sharing, a selective harmonic type virtual impedance, and a droop-based control are implemented at the primary level. Next, to reach better restoration and subsequently, seamless transition in accidental islanding, unintentional MG-DG’s outage, and synchronization process, the advanced three-phase SRF-PLL with in-loop MAF along with a simple adaptive lookup table are implemented in the secondary level of control. The MATLAB/Simulink simulation results verified that the proposed method improved the performance of control, effectiveness, and robustness in upstream or local grid variation.

An Advanced Proportional Multiresonant Controller for Enhanced Harmonic Compensation With Power Ripple Mitigation of Grid-Integrated PV Systems Under Distorted Grid Voltage Conditions

This article proposes an advanced integrated control strategy for enhanced grid current harmonic compensation with power ripple mitigation in a grid-integrated photovoltaic systems (GIPVS) under distorted grid voltage conditions. The proposed control strategy consists of an advanced proportional multiresonant (APMR) current controller and a compensator for grid voltage sag (CGVS), which is implemented with a phase-locked loop block. The APMR is designed in the α-β reference frame and minimizes the harmonics of the grid injected current. The CGVS, along with the APMR, eliminates the active and reactive power ripples under unbalanced voltage sags conditions. Further, an adaptive step size incremental conductance (ASINC) maximum power point tracking controller in integration with the proposed control strategy is implemented. Along with current harmonic reduction by APMR, the ASINC method ensures effective and faster tracking of maximum power point and negligible oscillations in the steady-state under different environmental conditions. By utilizing the proposed APMR control strategy, the frequency adaptability of the GIPVS is improved compared to the conventional proportional multiresonant (PMR) control strategy under grid frequency deviations. It successfully keeps the grid current total harmonics distortion below the acceptable limits for the grid voltage polluted by several odd harmonics, up to the nineteenth harmonics. The proposed control strategy of APMR with CGVS almost completely eliminates the power ripples in even severe unbalanced voltage sag conditions. Experimental studies are carried out using a real-time digital simulator to verify the effectiveness of the proposed control strategy in comparison with the conventional PMR controller.

A Dual Active Bridge Converter With Multiphase Boost Interfaces for Single-Stage Bidirectional DC–AC Conversion

A novel bidirectional dual active bridge based dc-ac converter is proposed in this article. The converter has multiphase boost interfaces at both the dc and ac ports. The interleaved operation of the multiphase units cancels the ripple currents and eliminates the input filter requirement. The dc to ac conversion is carried out in a single stage using only eight switches. The converter utilizes the low-frequency and high-frequency components in the inverter output to achieve both power conversion and power transfer across the high-frequency transformer simultaneously. A thorough analysis of the converter is carried out for the proper design of the components. Based on the results, a detailed design method is discussed. A multiresonant controller based phase-shift control is suggested to eliminate the low-frequency ripple in the input dc current. Finally, the effectiveness of the proposed converter is validated using results obtained from a 3-kW hardware prototype.

Guidelines for Single-Parameter Multiresonant Current Controllers Design Allowing Prescribed Magnitude Tracking of Periodic References

Unlike grid-connected and motor driving converters, typically exchanging sinusoidal current with the grid/motor, inverters employed in uninterruptible power supplies and active power filters generate periodic, harmonics-rich currents. Consequently, current controller in these applications must be capable of accurate tracking of references containing high harmonic count, calling for a multiresonant structure. On the other hand, major disturbances influencing the current loop comprise output and dc link voltages, which can typically be measured/estimated and cancelled by a feed-forward action. Thus, the current regulation problem is reduced to tracking challenge only. Recently, methodology for designing single-parameter single-resonant controllers according to desired tracking behavior of ac signal amplitude was proposed by the authors. However, as shown in the article, straightforward extension of the algorithm to multiresonant case is unfeasible. Nevertheless, it is possible to obtain an accurate approximation utilizing the decoupling property of resonant terms in both frequency and time domains. As a result, simple single-parameter multiresonant controller design guidelines are derived, imposing similar transient response to each individual harmonic of periodic reference. Simulations and experimental results validate the proposed design methodology.

Control of a Four-wire Hybrid Prosumer Converter for Balancing Utility Grids

Abstract The paper presents the project of the power electronic AC/DC converter operating under a multiresonant control algorithm for prosumer applications. This design allows independent control of active and reactive power for any or each phase. Both the converter and its algorithm are based on a three-phase converter of four-wire topology (AC/DC 3p-4w) with a DC bus, which couple the converter to a renewable energy source and energy storage. Further, model and simulation tests were carried out in the Matlab-SIMULINK programming environment. The results obtained indicate that operation with deep unbalances and powers of opposite signs in individual phases results in current variations (oscillations) in the DC line, which is a significant limitation, and it can be concluded that the level of asymmetry should be limited to the level acceptable to the energy storage device.

High performance current control of single‐phase grid‐connected converter with harmonic mitigation, power extraction and frequency adaptation capabilities

Grid-connected converters in distributed generation systems are required to operate under highly distorted voltage with a wide frequency range, and to provide active/reactive power information for ancillary services and power control. This paper presents multiple unbalanced synchronous reference frame control for regulating and mitigating the grid current distortion of a voltage source converter caused by grid voltage distortion and converter deadtime. The proposed control technique has intrinsic power extraction and frequency adaptation capabilities. The multiple unbalanced synchronous reference frame control is compared with the proportional multi-resonant control. A new controller which combines the unbalanced synchronous reference frame control for regulation of the fundamental component current and the multi-resonant control for harmonic compensation is presented. The proposed control techniques were verified with a 1.5-kVA LCL-filtered grid connected inverter. The multiple unbalanced synchronous reference frame control with odd harmonic orders 3rd to 13th exhibited excellent harmonic rejection with a total harmonic distortion (THD) less than 0.60% under a highly distorted voltage. The proposed combined control technique provided slightly inferior performance with the grid current THD less than 0.65%. The combined control scheme retains functionalities as the multiple unbalanced synchronous reference frame control with a significant reduction of computational effort.