Resonant Current Control Research Articles

Optimal hybrid resonant current controller for microgrids connected to an unbalanced IEEE test distribution network

Microgrids (MGs) based on renewable energies have emerged as a proficient strategy for tackling power quality issues in conventional distribution networks. Nonetheless, MG systems require a suitable control scheme to supply energy optimally towards the electrical grid. This paper presents an innovative framework for designing hybrid Proportional-Resonant (PR) controllers with Linear Quadratic Regulators (LQR), PR+LQR, which merge relevant properties of PR and LQR controllers. This method simultaneously determines the MG control parameters and the current unbalanced factor generated at the distribution network. We select the traditional IEEE 13-bus test feeder network and place two MGs at strategic locations to validate our approach. Moreover, we use the Grey Wolf Optimizer (GWO) to find control parameters through a reliable fitness function that leads to high-performance microgrids. Finally, we conceive several tests to assess the efficacy of GWO for tuning the hybrid controller and compare the resulting data across distinct realistic operation conditions representing power quality events. So, we choose four case studies considering different renewable energy penetration indexes and power factors and evaluate the effects of the MGs over the distribution grid. We also compare the proposed hybrid PR+LQR controller against closely-related alternatives from the literature and validate its robustness and stability through the disk margin approach and the Nyquist criterion. Our numerical simulations prove that hybrid controllers driven by GWO are highly reliable strategies, yielding an average unbalanced current reduction of 30.03%.

An optimized proportional resonant current controller based genetic algorithm for enhancing shunt active power filter performance

Current harmonics produced by nonlinear loads have destructive effects that affect the power quality of the power system and cause serious problems throughout the network. Active Power Filter (APF) is one of the best and most common solutions to reduce or eliminate harmonic disturbances; But due to the complexity and sensitivity of these filters, the accurate and fast performance of the control technologies used in it is the important and basic requirement. Therefore, by performing accurate and optimal adjustments for APF control, system performance and power quality level can be improved significantly. In this article, the design principles of Shunt Active Power Filter (SAPF) are introduced and the optimal control method of this system is explained by providing appropriate modeling. Also, as a suitable structure for the current control of the SAPF system, a Proportional-Resonant (PR) controller optimized by Genetic Algorithm (GA) is proposed. The PR controller with the capability of accurate tracking of harmonic currents and fast dynamic response is highly compatible with the SAPF system. In general, the goal is to achieve better and more appropriate performance to reduce harmonic disturbances and create a robust, faster, more accurate, flexible, stable, and optimal performance of these systems in detecting and generating compensation signals. The simulations have been done in MATLAB/SIMULINK, and also the experimental tests of this device have been done and validated in a real DSP-based SAPF. Finally, according to the results obtained under steady-state conditions with a favorable dynamic response, the Total Harmonic Distortion (THD) of the grid current has been significantly reduced from 20.2 % to 4.2 % for the R-L load and from 56.1 % to 4.5 % for the R-C load with a power factor of almost unity. These results confirm the optimal and standard performance of the proposed method.

Passivity-Based Design of Resonant Current Controllers Without Involving Partial Derivative

Passivity-Based Design of Resonant Current Controllers Without Involving Partial Derivative

A Single-Phase Seven-Level Triple Boost Inverter for Grid-Connected Transformerless PV Applications

A new seven-level common ground (CG) switched capacitor (SC)-based grid tied transformerless inverter has been introduced in this paper, which has three times boosting capability of input voltage. Thus, this inverter is preferable for low voltage PV applications without any boost conversion stage. To step-up the input PV voltage and facilitate seven steps in output voltage, two SC cells are connected in parallel. A virtual dc link capacitor serves key role for negative half cycle on behalf of H-Bridge and helping in constructing topology with common ground. The common grounding configuration of this inverter helps in bypassing the stray capacitance, which eliminates the leakage current and consequently reduces EMI considerably. Hence, further no requirement of any electro-magnetic interference (EMI) filter for electro-magnetic compatibility (EMC). Additionally, this inverter handles reactive power during the grid's lagging/leading power factor (pf) condition. To regulate active and reactive grid power, a proportional resonant (PR) current controller is designed. The proposed modulation scheme helps in balancing capacitor's voltages at their base values with allowable ripple. A detailed comparison also has been presented with other contemporary seven level inverters. The inverter circuit details, control technique, PWM scheme, thermal modeling, and loss analysis with component design guidelines are described in detail. Experimental results are presented to validate the effectiveness and feasibility of this proposed inverter.

Proportional Resonant Control With Phase Correction for Stability and Dynamics Enhancement Under Low Carrier Ratio Conditions

Phase-corrected proportional resonant (PCPR) current controllers are mainly studied under high carrier ratio conditions. When applied to high-power converters with low carrier ratios (LCR), the system could be unstable or have poor dynamics without a proper parameter design. In order to illustrate both stability and dynamics to guide parameter design, bilateral Bode plots are tailored in this paper that considers the correct negative jump direction at resonant frequencies. Then, this analysis tool verifies the feasibility of the phase correction angle set over 90°, especially under a carrier ratio below six. With the designed phase correction, the stability region of the carrier ratios is characterized as extending to the theoretical limit of one. Moreover, the resonant gain of PCPR is quantitatively designed considering the variation of carrier ratios by maximizing the bandwidth under guaranteed stability and margins. Finally, the simulations and experiments verify the enlarged stability region with the phase correction and improved dynamic performance with the proposed resonant gain design method.

Low voltage ride through control strategy for grid-tied solar photovoltaic inverter

Abstract This paper presents a low voltage ride through (LVRT) control strategy using an active power oscillations based reference current generation approach for grid tied solar photo voltaic (SPV) system under line-to-ground (LG) and double line-to-ground (LLG) faults. Proposed control strategy minimizes the harmonics injected into the grid, as well as oscillations in injected reactive power and DC-link voltage. Further this control strategy provides a dynamic control of active and reactive powers, the flow of sinusoidal currents into the grid, and avoids the disconnection between the utility grid and SPV system during faults. A proportional resonant (PR) current controller is developed in a stationary reference frame to achieve the power quality by fulfilling the grid codes. Simulation and experimental results are presented to highlight the merits of the proposed control scheme.

A Novel Single Phase Three Level Triple Boost CG Switched-Capacitor Based Grid-Connected Transformerless PV Inverter

A new three-level inverter based on the switched capacitor (SC) with a common grounding (CG) configuration has been introduced in this article, which is capable of boosting the input voltage up to three times. Therefore, this inverter is configured without any boost dc/dc converter stage for low voltage PV application. To step up the input PV voltage and facilitate three level in output voltage, two SC cells are connected in parallel. This inverter's common grounding configuration helps in bypassing the stray capacitance, which eliminates the leakage current and consequently reduces electro-magnetic interference (EMI) considerably. Hence, for electro-magnetic compatibility (EMC), this inverter does not require any EMI filter. Additionally, this inverter handles reactive power during the grid's lagging/leading power factor (pf) condition. A proportional resonant (PR) current controller is designed to regulate active and reactive grid power. The proposed modulation strategy helps in balancing capacitor voltages at their base values with allowable ripple. The inverter circuit details, control technique, PWM scheme, thermal modeling, and loss analysis with component design guidelines are described in detail. Experimental results are presented to validate the effectiveness and feasibility of this proposed inverter.

Coordination Control of a Hybrid AC/DC Smart Microgrid with Online Fault Detection, Diagnostics, and Localization Using Artificial Neural Networks

In this paper, a solar and wind renewable energies-based hybrid AC/DC microgrid (MG) is proposed for minimizing the number of DC/AC/DC power conversion processes. High penetration rates of renewable energy increase MG instability. This instability can be mitigated by maintaining a balance between consumption demand and production levels. Coordination control is proposed in this study to address coordinated electricity flowing through both AC and DC links and to achieve system stability under variability of generation, load, and fault conditions. The MG adopts a bidirectional main converter that is controlled using a digital proportional resonant (PR) current controller in a synchronous reference frame. The PR controller plays a role as a digital filter with infinite impulse response (IIR) characteristics by virtue of its high gain at the resonant frequency, thereby reducing harmonics. Moreover, the applied PR controller quickly follows the reference signal, can adapt to changes in grid frequency, is easy to set up, and has no steady-state error. Moreover, the solar photovoltaic (PV)-based distribution generation (DG) is supported by a maximum power point tracker (MPPT)-setup boost converter to extract maximum power. Due to the usage of converter-connected DG units in MGs, power electronic converters may experience excessive current during short circuit faults. Fault detection is critical for MG control and operation since it empowers the system to quickly isolate and recover from faults. This paper proposed an intelligent online fault detection, diagnostic, and localization information system for hybrid low voltage AC/DC MGs using an artificial neural network (ANN) due to its accuracy, robustness, and quickness. The proposed scheme enables rapid detection of faults on the AC bus, resulting in a more reliable MG. To ensure the neural network’s validity, it was trained on various short circuit faults. The performance of the MG was evaluated using MATLAB software. The simulation findings indicate that the suggested control strategy maintains the dynamic stability of the MG, meets the load demand, and achieves energy balance as well as properly predicts faults.

Comparative Stability Analysis and Improvement of Grid-Following Converters Using Novel Interpretation of Linear Time-Periodic Theory

This article presents a comparative stability investigation of grid-following (GFL) converters with different advanced phase-locked loops (PLLs) and current control schemes based on linear time-periodic (LTP) theory. First, a time-domain physical interpretation of the LTP theory is proposed, which inspires an iterative LTP eigenvalue computation algorithm. A measure for the influence of the frequency coupling effect on each eigenvalue is defined to demonstrate the necessity of applying the LTP theory. Then, eigenvalue-based stability analysis is carried out to gain insights into dynamic characteristics of two implementations of GFL converters, namely, dual synchronous reference frame PLL (DSRF-PLL) and proportional integral (PI) current control, and dual second-order generalized integrator PLL (DSOGI-PLL) and proportional resonant (PR) current control. The effects of the PLL bandwidth, the current control time constant, the grid strength, and imbalance on the system stability are evaluated. In addition, a damping loop is proposed to improve the stability margin of GFL converters connected to weak grids. Finally, MATLAB/Simulink simulations and experimental measurements validate the correctness of the proposed modeling method and stability assessment results.

Digital Resonant Current Controller for LCL-Filtered Inverter Based on Modified Current Sampling and Delay Modeling

In this article, a digital resonant current controller is proposed for pulsewidth modulation (PWM) control of an LCL-filtered inverter based on a modified current sampling method and time delay modeling. Since the current sampling technique employed here uses a freely tunable sampling instant within the PWM signal period, a corresponding LCL filter model discretization technique is used based on a modified Z-transform. This is applied to model the fractional delay introduced by the current sampling technique, which uses sampling instants from within the PWM signal period. Modified Z-transform-based delay modeling has not previously been employed for LCL-filtered inverters, although it has been used in inverters with an RL load. The proposed technique is implemented with a fifth-order current controller, which directly controls the power converter ac output current without the need for active damping, as is typical for converters with LCL filters. A method based on pole placement is adopted to tune the controller parameters, in which the positions of all the closed-loop poles of the control system are determined. The responses of the controller to reference and disturbance signals are analyzed through simulation and experimental testing for different sampling instants within the PWM signal period.

Control of multifunctional inverter to improve power quality in grid-tied solar photo voltaic systems

Abstract In this paper, a control algorithm is proposed for a multifunctional inverter to improve power quality in a grid-tied solar photo voltaic (SPV) systems connected to non-linear and unbalanced loads. During light loads and low solar irradiance, the surplus capacity of inverter rating is optimally utilized to compensate some of the power quality (PQ) indices based on conservative power theory (CPT) along with active power injected into the utility grid and also connected loads. The stationary reference frame based proportional resonant (PR) current controller is designed to facilitate accurate tracking of inverter currents, fast time response under dynamic conditions when unbalanced and non-linear loads are connected at the point of common connection (PCC). The proposed control scheme enables selective compensation of power quality indices such as harmonics, unbalance and reactive powers depending on type of load and grid requirements there by, reducing the burden on the utility grid. Experimental results for various dynamic conditions are presented to validate the proposed controller performance and highlight the merits.

An Enhanced Control Strategy to Mitigate Grid Current Harmonics and Power Ripples of Grid-Tied PV System Without PLL Under Distorted Grid Voltages

This article proposes an enhanced integrated control strategy to mitigate grid current harmonics and power ripples for a three-phase grid-tied photovoltaic (GTPV) system without a phase-locked loop (PLL) unit. The proposed control strategy consists of an enhanced proportional resonant (EPR) current controller, which suppresses the harmonics of grid injected current under distorted grid voltage conditions. A phase compensated reference current generator (PCRCG) is integrated with the proposed EPR controller and used to eliminate active and reactive power oscillations under grid voltage sags and swells. The proposed integrated control strategy is implemented in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha \beta $ </tex-math></inline-formula> stationary reference frame. The synchronization task is included in the PCRCG and making the system PLL-less. Thus, the associated computational burden and implementation complexity are reduced. Furthermore, the frequency adaptability of the GTPV system is enhanced as compared with the PLL-based control strategy in the presence of grid frequency variations using the proposed control strategy. To ensure the fast maximum power point (MPP) tracking, a modified incremental conductance MPP tracking algorithm is implemented in integration with the proposed control strategy. The effectiveness of the proposed control strategy is validated using OPAL-RT real-time digital simulator and compared with the conventional PLL-based control strategy.

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.

A new digital resonant current controller for AC power converters based on the advanced Z-transform

In this paper, we present a new digital resonant current controller that can be applied in single-phase and three-phase alternating current (AC) power converters, based on voltage source inverters (VSI) with pulse width modulation (PWM). Since power converters based on PWM introduce fractional time delays regarding the sampling period (Ts), because of the current sampling and PWM command updating techniques that are employed, there is a need to develop analytical tools for precise modelling of these types of delays. To achieve this, the advanced Z-transform is applied in order to model the AC controllers in VSIs with PWM for the general case of a fractional time delay, including power converters with current sampling within a PWM period at any chosen time instance. This new approach to power converter modelling and current sampling allowed us to develop a modified resonant AC current controller for a VSI with RL load, based on the pole-placement parameter tuning method. It includes fractional time delays, which are conventionally employed in the power converter design, in the controller parameter derivations, and introduces the minimal order resonant controller that enables strict placement of all closed-loop control system poles. Simulations and experimental tests are carried out to show the improvements introduced by novel solution in this paper compared with conventional resonant current controllers. In the analysis of dynamic performance and robustness, in this paper conventional indices are applied to compare the proposed controller with a conventional design.

Optimal Resonant Current Controller for Microgrids Connected to Unbalanced Ieee Test Distribution Network Using Grey Wolf Optimizer

Optimal Resonant Current Controller for Microgrids Connected to Unbalanced Ieee Test Distribution Network Using Grey Wolf Optimizer

Resonant Current Regulator Implemented in the Discrete-Time Domain for Grid-Connected Converters

Effective current control is an aspect of paramount importance to achieve a high level of performance for grid-connected converters (GCCs). A common practice is to first develop a continuous-time controller and then convert it to a discrete equivalent using one of the discretization techniques available. However, determining the optimum choice is elaborating, and the performance of the discretized controller has been shown degraded performance compared to that of continuous version, especially for cases in which switching frequency is relatively low with respect to the excitation frequency. The principle of the current controller design in the discrete-time domain has been comprehensively addressed in this work, which can be summarized as three major steps. The first step is to develop the controller in the positive-sequence synchronous reference frame (PS-SRF), by canceling the weakly damped pole of the plant with a matching zero and providing infinite open-loop gain for the dc current in the PS-SRF. Then, the corresponding controller for the negative-sequence current regulation can be derived, following a similar procedure. Based on the double SRF control (DSRFC), the resonant current controller implemented in the stationary reference frame can be finally developed. In this manner, the discretization is avoided, and the one-sampling delay and the zero-order holder characteristic of the converter can be considered in the developed controller, which means that the additional delay compensation strategy can be avoided. Experimental results have verified the effectiveness of the proposed controller for the current regulation of GCCs under different grid conditions. It should be noted that the proposed method can also be applied to other applications, such as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LCL$ </tex-math></inline-formula> -filtered grid-connected or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> -filtered grid-forming converters with proper active damping although only the simpler <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$L$ </tex-math></inline-formula> -filtered GCC is analyzed as an example in this work.

Design and Analysis of Controller with Selective Harmonic Compensator for Grid Connected PV System

Harmonics produced by distributed power generation systems (DPGS) is a main power quality issue, particularly due to the number of these systems connected to the grid is always increasing. This means that, it is significant to control the harmonics caused by these inverters to limit their contrary effects on the grid power quality. This paper has proposed a new proportional current controller (P Resonant Current Controller) with selective harmonic compensator for grid connected photovoltaic (PV) systems. The proportional resonant current controller (PRCC) can have a significant effect on the quality of the current supplied to the grid by the PV inverter, and hence it is essential that the controller provides a high-quality sinusoidal output with negligible distortion to avoid generating harmonics. The effectiveness of the proposed framework has been verified using simulation results in MATLAB/Simulink.

Power Quality Enhancement Using Dynamic Voltage Restorer (DVR)-Based Predictive Space Vector Transformation (PSVT) With Proportional Resonant (PR)-Controller

In the power distribution system, the Power Quality (PQ) is disturbed by the voltage sag and swells. The Dynamic Voltage Restorer (DVR) is used to enhance various PQ problems like voltage sag, swells, and Harmonics. The previous Intrinsic Space Vector Transformation (ISVT) control techniques with DVR system, to compensate the power quality issue. It produced a steady-state error, low efficiency, and high THD. The SMES based DVR has provided excellent results in overcoming these issues. The energy is stored by DVR through a storage element, which takes alternate energy from a Solar PV cell. The Maximum Power Point Tracking (MPPT) based P&O algorithm is implemented to equalize the solar power. The Voltage Source Inverter (VSI) generates the reactive power, which has to be compensated with the help of Pulse Width Modulation (PWM) and the feedback control loop are essential to enhance the injection of reactive power to the line. Due to this reason, a proposed Predictive Space Vector Transformation (PSVT) control-based DVR is implemented. It analyzes the variation of power on the distribution side and generates the proper feedback control to the inverter systems. In the instant of voltage injection to the line with the help of DVR, the phase angle mismatch happens which is not synchronized reactive power to the grid. Due to the non-synchronization of reactive power, more harmonic distortion is generated. A Proportional Resonant (PR) controller is introduced, which is Proportional Resonant (PR) current controller. The current injected by the inverter into the grid in phase with the grid voltage maintain constant with unity power factor. The PR controller design is cascaded with a harmonic compensator to mitigate low order odd harmonic components present in the output current of VSI and minimize the total harmonic distortion (THD). The performance of the proposed is evaluated using MATLAB 2017b software.

A Study on Driving Algorithm of Single-phase PMSM based on Proportional Resonant Current Controller

A Study on Driving Algorithm of Single-phase PMSM based on Proportional Resonant Current Controller