A DQ synchronous frame controller for single-phase inverters

Applied Sciences, 2020

This work proposes a power control strategy based on the linear quadratic regulator with optimal reference tracking (LQR-ORT) for a three-phase inverter-based generator (IBG) using an LCL filter. The use of an LQR-ORT controller increases robustness margins and reduces the quadratic value of the power error and control inputs during transient response. A model in a synchronous reference frame that integrates power sharing and voltage–current (V–I) dynamics is also proposed. This model allows for analyzing closed-loop eigenvalue location and robustness margins. The proposed controller was compared against a classical droop approach using proportional-resonant controllers for the inner loops. Mathematical analysis and hardware-in-the-loop (HIL) experiments under variations in the LCL filter components demonstrate fulfillment of robustness and performance bounds of the LQR-ORT controller. Experimental results demonstrate accuracy of the proposed model and the effectiveness of the LQR-O...

2012 IEEE Energy Conversion Congress and Exposition (ECCE), 2012

Due to the growing changes in the electrical network related to the new distributed generation scheme and the integration of renewable energy sources, new requirements for grid-connected power converters are being defined in the new grid codes. The injection of positive-and negativesequence current components is becoming necessary for achieving new capabilities like the reactive power injection during a grid fault. This paper deals with a fundamental issue in this topic, i.e., the performance of the current controller. Classical dq controllers, which are extensively used in industrial applications, degrade its performance when both sequences are involved, as unavoidable oscillations in the dq axes appear. In this paper, a new scheme for controlling positive-and negative-sequence currents using dq controllers is proposed, based on an enhanced Double Synchronous Reference Frame (DSRF) controller. In this paper the DSRF controller is improved by adding a decoupling network which counteracts the oscillations caused by the presence of both sequences. Experimental results will demonstrate the validity of the proposed Decoupled DSRF (DDSRF) controller.

IEEE Transactions on Power Electronics, 2000

In the last years, restrictive grid codes have arisen to ensure the performance and stability of electrical networks, which are experiencing a massive integration of renewable energy sources and distributed generation systems, that are normally connected to the grid through electronic power converters. In these codes the injection of positive-and negativesequence current components is becoming necessary for fulfilling, among others, the low voltage ride-through requirements during balanced and unbalanced grid faults. However, the performance of classical dq current controllers, applied to power converters, under unbalanced grid voltage conditions is highly deficient, due to the unavoidable appearance of current oscillations. This paper analyses the performance of the double synchronous reference frame (DSRF) controller and improves its structure by adding a decoupling network for estimating and compensating the undesirable current oscillations. Experimental results will demonstrate the validity of the proposed decoupled DSRF (DDSRF) controller.

Energies, 2020

In many countries the percentage of power electronic interfaced power sources (PEIPS), especially renewable energies like wind power and photovoltaic (PV), has increased significantly during the last decade.Retaining system stability with a declining number of conventional synchronous generators is a new challenge that starts to be addressed by Grid Operators. The existing control schemes used in distributed energy generation inverters generally do not provide significant services to grid stability. This paper focuses on a control scheme that is in many ways similar to the control of conventional power plants, but avoids a higher rating of the inverters which is often required by control approaches emulating the response of a synchronous generator. The control parameters of the proposed scheme are derived analytically and their main dependencies from major system parameters are discussed. An add-on to achieve fault ride through capability for both balanced and unbalanced faults for voltage controlled inverters is presented. Model validation results in a laboratory setup show very good correlation and have proven practicability of the theory as well as fault ride through and islanding capability.

IEEE Access, 2025

This paper introduces a novel single-loop control scheme for voltage regulation in islanded inverters, using a proportional-integral-lead (PI-Lead) controller designed within the synchronous reference frame (SRF) through a loop-shaping approach. Commonly, dual-loop controllers have been employed for this purpose owing to several limitations, such as insufficient stability with a narrow gain margin, a trade-off between stability and bandwidth, and constrained bandwidth due to the need for a significantly lower outer voltage loop bandwidth compared to the inner current one. The proposed method overcomes these challenges by integrating a Lead compensator, which enhances voltage regulation by eliminating steady-state error, improving stability margins, and providing a fast transient response while maintaining robustness against model parameter variations. Additionally, the control strategy reduces dependence on current measurements, except when dealing with inductive loads where virtual resistor-based active damping is necessary. Despite the challenges posed by multi-resonance phenomena and coupling effects inherent in single-loop SRF-based modeling, a comprehensive frequency-domain analysis is performed, with systematic controller parameter design guidelines to mitigate multi-gain crossover issues. Rigorous experimental results validate the theoretical findings and simulations, demonstrating the superior performance and practical effectiveness of the proposed control strategy compared to existing methods.

Journal of Power Electronics, 2016

Small distributed generating units are usually connected to the main electric grid through single-phase voltage source inverters. Grid operating conditions as voltage and frequency are not constant and can fluctuate within the range values established by the International Standards; furthermore, the requirements in terms of power factor correction, total harmonic distortion, and reliability are getting tighter day by day. As a result, the implementation of reliable and efficient control algorithms, which are able to adjust control parameters to the changeable grid operating conditions, is essential. This paper investigates the configuration topology and the control algorithm for a single-phase inverter with the purpose of achieving high performance in terms of efficiency as well as total harmonic distortion of the output current. Accordingly, a Second Order Generalized Integrator with a suitable Phase Locked Loop (SOGI-PLL) is at the basis of the proposed current and voltage regulation. Some practical issues related to the control algorithm are addressed too, and a solution for the control architecture is proposed, based on Resonant Controllers continuously tuned on the basis of the actual grid frequency. Further, intentional islanding operation is investigated and the possible procedure for the switchover from grid-tied to islanding operation and vice-versa is proposed.

International Journal of Power Electronics and Drive Systems (IJPEDS), 2021

Because of its simplicity and autonomous operation, droop control technique is widely implemented for power generation control in microgrids. Despite its popularity, it has been reported that the technique has the stability problem. In this paper, the previous work of droop-free inverter-based generator designed for operating in a fix frequency islanded microgrid, is redesigned to have the ability to operate in both islanded and grid connected microgrid as well as to the main power grid where it interconnected with synchronous generators. The proposed voltage source inverters use phase locked loop (PLL) algorithm to synchronize the changing frequency due to the operation of the synchronous generator. Unlike the frequency droop control that the output frequency is varied as its active power changed, the proposed controls do not make an adjustment of the system frequency. This kind of operation reduces the chance of the system unstable due to severe frequency change and it also reduces the frequency deviation when it increases its active power output. Simulation and result of the meshed power network demonstrate the feasibility to implement the proposed controls in the real system.

IEEE Transactions on Power Electronics, 2000

A control technique is developed for a three-phase four-wire split dc bus inverter of a single distributed generation unit working in island mode. The control technique combines an inner discrete-time sliding mode controlled (DSMC) current loop and an outer robust servomechanism controlled voltage loop. The control algorithms are developed under stationary 0 (Clarke's) reference frame and a modified space vector pulsewidth modulation (MSVPWM) is proposed to implement the algorithm under Clarke's reference frame. The proposed technique achieves voltage regulation with low steady state error and low total harmonic distortion and fast transient response under various load disturbances. Meanwhile the usage of MSVPWM in a stationary 0 reference frame yields better transient performance under limited dc bus voltage compared to conventional uniformly sampled sine wave modulation in reference frame. In this paper, besides the development and description of the algorithms, a series of discussions, analysis and studies are performed on the proposed control technique, including the -filter design issue, frequency domain closed-current-loop and closed-voltage-loop responses, and time domain simulations and experiments under various load conditions. All the analysis, simulations, and experiments demonstrate the effectiveness of the proposed control solution.

In this paper islanding operation of a voltage source converter based DG system with fuzzy logic controller is presented. In the grid-connected mode, a microgrid including its loads and DG units is connected to the main grid at the point of common coupling (PCC), the voltage-sourced converter is operated in the active and reactive power (PQ) control mode, by using conventional control scheme to control the active and reactive power exchange with the grid. In the islanded mode, the proposed ANFIS is used to control the voltage of the islanded system despite the load variability and uncertainties. The salient features of the proposed ANFIS are: 1) efficient to deal with the nonlinear systems 2) design does not depend on the mathematical model of the system and 3) less sensitive to the parameters variation than the conventional controllers. The frequency of the islanded system is dictated through the use of an internal oscillator. The simulation results are presented by using Matlab/simulink platform. The dynamic response of the DG system using the ANFIS have good transient behaviors compairing to the FLC and PI controllers.

Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting, 2006

In this paper, different control structures applied to distributed power generation system are discussed. Implementation of proportional-integral (PI), proportional-resonant (PR), hysteresis and dead beat controller in different reference frames is also treated. An evaluation in terms of current harmonic distortion when running in steady state condition is made. Additionally, the controllers behavior in transient operation such as step in current reference and single phase fault in the utility grid has also been studied. Experimental results are presented for their evaluation.