scholarly journals A Theoretical Concept of Decoupled Current Control Scheme for Grid-Connected Inverter with L-C-L Filter

2021 ◽  
Vol 11 (14) ◽  
pp. 6256
Author(s):  
Mohamad Amin Ghasemi ◽  
Seyed Fariborz Zarei ◽  
Saeed Peyghami ◽  
Frede Blaabjerg
Keyword(s):  
Control Method ◽  
Controller Design ◽  
Current Control ◽  
System Stability ◽  
State Equations ◽  
Lcl Filter ◽  
Control Scheme ◽  
Grid Connected Inverter ◽  
The Stability ◽  
Grid Side

This paper proposes a nonlinear decoupled current control scheme for a grid-connected inverter with LCL filter. Decoupling the active and reactive current control channels is one of the main demands in the control of inverters. For inverters with an L filter, the decoupling can be achieved by a proper feed-forward of grid voltages. However, the coupling of channels is a complex issue for converters with LCL filters. The resonance mode of the LCL filter may cause instability, which adds more complexity to the analysis. In this paper, state equations of the system are provided, which highlight the coupling between active and reactive currents injected into the grid. Accordingly, a non-linear control scheme is proposed which effectively decouples the channels and dampens the resonant modes of the LCL filter. The stability of the proposed control method is verified by the Lyapunov criterion. Independency of the system stability to the grid-impedance is another feature of the proposed approach. Moreover, only grid-side currents are needed for implementation of the proposed scheme, avoiding the need for additional current sensors for the output capacitor and grid-side inductor. For accurate modelling of the inverter, the computation and PWM sampling delays are included in the controller design. Finally, various case studies are provided that verify the performance of the proposed approach and the stability of the system.

scholarly journals Current Control and Active Damping for Single Phase LCL-Filtered Grid Connected Inverter

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Mohammad Alshiekh ◽  
Alaa Marouf ◽  
Muhieddin Kubeitari
Keyword(s):  
Current Control ◽  
Active Damping ◽  
System Stability ◽  
Switching Frequency ◽  
Control Loop ◽  
Passive Element ◽  
Lcl Filter ◽  
Control Scheme ◽  
Grid Connected Inverter ◽  
Filter Capacitor

LCL filter has been widely used in the grid connected inverter, since it is effective in attenuation of the switching frequency harmonics in the inverter. However, the resonance in this filter causes stability problems and must be damped effectively to achieve stability. There are some methods to damp the resonance; one method is passive damping of resonance by adding a series resistor with the filter capacitor, but passive element reduces the inverter efficiency. Other method uses active damping (AD) by adding a proportional control loop of filter capacitor current, but this method needs additional sensor to measure filter capacitor current; moreover, when the control loops are digitally implemented, the computation delay in AD control loop will lead to some difficulties in choosing control parameters and maintaining system stability. This paper presents current control scheme for the grid connected inverter with the LCL filter. The proposed scheme ensures the control of injected current into grid with AD of the resonance in the LCL filter while keeping system stability and eliminating the effect of computation delay of the AD loop. An estimation of filter capacitor current with one step ahead is performed using the discrete time observer based on measuring the injected current. This reduces the cost and increases the robustness of the system. Proportional Resonant (PR) controller is used to control the injected current. Design of control system and choosing its parameters are studied and justified in details to ensure suitable performance with adequate stability margins. Simulation and experimental results show the effectiveness and the robustness of the proposed control scheme.

A Control Method to Suppress Resonance and Improve Current Quality for Inverter System with LCL Filter

2014 ◽  
Vol 644-650 ◽  
pp. 3528-3533
Author(s):  
Yong Peng Lin ◽  
Shun Tao ◽  
Xiang Ning Xiao ◽  
Mei Rong Wu
Keyword(s):  
Control Method ◽  
Current Control ◽  
Utilization Efficiency ◽  
Control Effect ◽  
Lcl Filter ◽  
Loop Control ◽  
Grid Voltage ◽  
Grid Current ◽  
Differential Voltage ◽  
Grid Side

The LCL filter is easy to resonate, especially in the new energy power system with multiple inverters. The LCL filter resonant formulas are derived in this paper and a novel double closed loop control strategy combing with the structure of the LCL filter was proposed at the base on feedback of capacitor current as a result. In the control system, the inner loop feedback the first differential voltage of filter inductor at the grid side to damp the resonance and nature of first differential voltage of filter inductor is explained; the grid current outer loop achieves direct control of the grid current for high power factor and utilization efficiency. The simulation results show that the grid-side inductor voltage differential feedback control have a better current control effect both in the condition of the normal power grid voltage and distorted grid voltage, and the fluctuations of power and dc voltage are reduced.

scholarly journals Discrete-Time DC-Link Voltage and Current Control of a Grid-Connected Inverter with LCL-Filter and Very Small DC-Link Capacitance

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5613 ◽  
Author(s):  
Oliver Kalmbach ◽  
Christian Dirscherl ◽  
Christoph M. Hackl
Keyword(s):  
Discrete Time ◽  
Controller Design ◽  
Linear Quadratic Regulator ◽  
Current Control ◽  
Control Loop ◽  
Linear Quadratic ◽  
Lcl Filter ◽  
Current Controller ◽  
Voltage Controller ◽  
Grid Connected Inverter

The paper presents a controller design for grid-connected inverters (GCI) with very small dc-link capacitance that are coupled to the grid via an LCL filter. The usual controller designs would fail and result in instability. The proposed controller has a cascaded structure with a current controller as inner control loop and an outer dc-link voltage controller. The controller design is performed in discrete time and it is based on a detailed stability analysis of the dc-link voltage controller to determine the controller parameters which guarantee stability for all operating points. The inner loop is a state-feedback current controller that is designed based on the discrete linear-quadratic regulator (DLQR) theory. An additional integral error feedback assures steady-state accuracy of the current control loop. The simulation and experimental results validate performance and stability of proposed controller design.

A bilateral control scheme for vehicle steer-by-wire system with road feel and steering controller design

2017 ◽  
Vol 41 (3) ◽  
pp. 593-604 ◽  
Author(s):  
Hongyu Zheng ◽  
Jinghuan Hu ◽  
Yahui Liu
Keyword(s):  
Controller Design ◽  
Steering System ◽  
System Stability ◽  
Steering Wheel ◽  
Bilateral Control ◽  
Loop Control ◽  
Control Scheme ◽  
Steer By Wire ◽  
The Stability ◽  
Close Loop Control

Steer-by-wire (SBW) system replaces the mechanical linkages in a conventional steering system with electronic actuators. However, such a steering system has problems regarding how to harmonize angle and torque close loop control strategy whilst guaranteeing SBW system stability. Towards this problem, a bilateral control scheme is proposed for SBW system with steering and road feel feedback control. A new torque and angle feedback deviation type bilateral control scheme is designed based on the analysis of several typical bilateral control schemes. In this bilateral control scheme, it only needs to measure steering wheel angle, steering wheel torque, pinion angle and steering motor torque, whilst it does not need to estimate tire and road force, neither to deploy complicated and expensive sensors or devices. The Llewellyn stability criterion and wave variable control are used to analyze the influencing factors of the stability of the SBW system and to control the stability respectively. The transparency of the SBW system is analyzed based on the impedance theory. In order to improve vehicle handling, the road feel feedback torque is designed by using a compensation controller. The bilateral control scheme and compensation controllers are implemented and their performance is experimentally validated using test vehicle. Test results demonstrate the efficiency and effect of the proposed algorithm.

scholarly journals Stability Assessment of Current Controller with Harmonic Compensator for LCL-Filtered Grid-Connected Inverter under Distorted Weak Grid

2020 ◽  
Vol 11 (1) ◽  
pp. 212
Author(s):  
Seung-Jin Yoon ◽  
Thuy Vi Tran ◽  
Kyeong-Hwa Kim
Keyword(s):  
Closed Loop ◽  
Current Control ◽  
System Stability ◽  
Stability Assessment ◽  
Weak Grid ◽  
Current Controller ◽  
Distorted Grid ◽  
Grid Impedance ◽  
Grid Connected Inverter ◽  
The Stability

An assessment of the stability and performance of current controllers with harmonic compensators is presented for an inductive-capacitive-inductive (LCL)-filtered grid-connected inverter under distorted weak grid conditions. By using two typical current control schemes which are the direct current controller with the capacitor current-based active damping and integral-resonant state feedback current controller, the closed-loop system stability and current control performance are investigated in the presence of both uncertain grid impedance and distorted grid. Even though the controller stability has been investigated under weak grid in several studies, the stability assessment of the entire current control scheme, including the harmonic resonant controllers, still needs a further comprehensive investigation. The system stability is analyzed by obtaining the movement of the closed-loop poles in the discrete-time domain when the grid impedance varies. To fully study the impact of distorted weak grid condition on the LCL filters, three LCL filter parameter sets giving the resonance frequency in different frequency bands are chosen for the purpose of evaluating the system robustness and grid-injected current quality. In order to support the presented theoretical analyses, comprehensive simulation and experimental results based on 32-bit DSP TMS320F28335 to control 2 kVA grid-connected inverter are presented in terms of grid current quality and control stability in the environment of both uncertain grid impedance and distorted grid.

scholarly journals A NOVEL METHOD FOR DESIGNING THE CONTROLLER OF A LCL-FILTER-BASED GRID-CONNECTED INVERTER WITH CONSIDERING VARYING SYSTEM PARAMETERS

2018 ◽  
Vol 54 (3A) ◽  
pp. 39
Author(s):  
Nguyen Trung Nhan
Keyword(s):  
Controller Design ◽  
Design Method ◽  
Lcl Filter ◽  
Loop Control ◽  
System Parameters ◽  
Three Phase ◽  
Loop Control System ◽  
Novel Method ◽  
Grid Connected Inverter ◽  
The Stability

Exactly determining the control coefficients for the controller of a three-phase LCL-filter-based inverter is an important and challenging issue in microgrid systems. However, existing LCL-filter-based inverter systems usually assume that all system parameters are determined accurately and remain constant over time, which is not true in real situations. Variations in the system parameters are known to possibly seriously degrade the performance of LCL-filter-based inverter systems. For efficiency and robustness, this paper proposes a novel method for the generalized controller design of a three-phase LCL-filter-based grid-connected inverter system that can address deviations in system parameters. An optimum way to determine the stability bounds under various system parameters cases is introduced. The assessment of the stability bounds is based on the Routh criterion by solving the characteristic equation of the closed-loop control system. Simulations results are presented to validate the correctness and effectiveness of the proposed design method.

scholarly journals A novel current controller design for grid-integrated PV inverter system

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Ayaz Ahmad ◽  
L. Rajaji ◽  
A. Iqbal
Keyword(s):  
Controller Design ◽  
Vital Role ◽  
Current Feedback ◽  
Lcl Filter ◽  
Design Algorithm ◽  
Grid Voltage ◽  
Pv Inverter ◽  
Current Controller ◽  
Experimental Implementation ◽  
Grid Connected Inverter

AbstractDistributed generators are playing a vital role in supporting the grid in ever-increasing energy demands. Grid code regulation must be followed when integrating the photovoltaic inverter system to the grid. The paper investigates and analyzes a controller model for grid-connected PV inverters to inject sinusoidal current to the grid with minimum distortion. To achieve better tracking and disturbance rejection, a DSP-based current controller is designed with LCL filter. The controller gets the current feedback from the grid, compares it with reference current, and calculates duty cycle to generate PWM pulses to trigger H-bridge converters. The grid voltage is loaded to the initial value in proposed PR controller to ensure the initial inverter voltage to match the grid voltage. The paper presents a novel current controller algorithm for grid-connected inverter system, and simulation is done. A detailed analysis has been carried out to validate the proposed design algorithm. Experimental implementation of the current controller in the DC/AC converter circuits with an LCL filter is done for 5.4 kW to validate and match the simulation model.

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