Aalborg Universitet Improved control strategy for the three-phase grid-connected inverter (original) (raw)
Related papers
Renewable Energy Focus, 2017
In this paper, an overview of grid-connected renewable systems is presented, then two current-control strategies for 3-phase grid-connected inverters are analyzed: firstly, the well-known d-q control in the rotating synchronous reference frame (d-q axes) using Proportional Integral regulators is described, and secondly, the Proportional Resonant controller in the Stationary Reference Frame (ab axes). In order to obtain a high efficiency of the system when the 3-phase utility grid voltages are affected by harmonic pollution, a Harmonic Compensator (HC) structure is used with the Proportional Resonant controller, this due to the ease way to compensate harmonics when a Proportional Resonant control is utilized instead of a d-q control. Then both control strategies (d-q control and PR + HC) are analyzed under harmonic pollution condition. For both strategies, a Positive Sequence Detector plus a Synchronous Reference Frame Phase-Look Loop (PSD + dqPLL) is used as the synchronization algorithm. After the study, it was observed that the PR controller provides a greater facility for carrying out the harmonic compensation process helping to fulfill with the international standards. A model of a grid-connected photovoltaic system with a nominal power of 10 kW is used to evaluate and compare the performance of the current-control strategies. For this, a Real-Time Digital Simulator (RTDS) platform is used.
IJERT-An Improved Control Scheme for Grid Connected Voltage Source Inverter
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/an-improved-control-scheme-for-grid-connected-voltage-source-inverter https://www.ijert.org/research/an-improved-control-scheme-for-grid-connected-voltage-source-inverter-IJERTV3IS041935.pdf In grid connected Distribution Generation systems, Voltage Source Inverters are used for interfacing the renewable energy source to the utility grid. DG has variety of problems during grid integration. Hence the control of the grid connected inverter plays an important role in feeding a grid with high quality power. This report presents an analysis of the stability problem of a grid connected with Voltage Source Inverter and with a LC filter. The possible grid-impedance variations have a significant influence on the system stability. Whenever the grid inductive impedance increases, the low frequency gain and the bandwidth of the Proportional Integral (PI) controller have to be decreased to maintain the system stable, thereby degrading the tracking performance and disturbance rejection capability. To overcome this problem an H∞ controller is proposed with an explicit robustness in terms of grid impedance variations to incorporate the desired tracking performance and stability margin. The proposed method is simulated by using MATLAB/SIMULINK. The results of the proposed H∞ controller and the conventional PI controller are compared, which validates the performance of the proposed control scheme. Keywords-Distributed Generation (DG), Voltage Source Inverter (VSC), LC Filter, H∞ Controller, Total Harmonic Distortion (THD). I.INTRODUCTION Increasing demand for electricity under limited availability and supply from conventional resources has resulted in an energy crisis. Each and every development in the present age depends mainly on the electrical energy. To have sustained and continuous development, the depletion of non-renewable sources should be compensated with some other sources of energy. A feasible solution to this problem is to generate energy from a renewable resource wherever it is available and utilize it to meet the demands. IEEE defines Distributed Generation (DG) as the generation of electricity by facilities that are sufficiently smaller than central generating plants so as to allow interconnection at nearly any point in a power system. The utilization of environmentally clean Renewable Energy Sources (RES) results in improved reliability and energy security for the existing power system network. As the distributed energy sources are very close to the utility systems, transmission losses are reduced to a great extent. The distributed generation has other advantages as well improved grid asset utilization, reduced Transmission and Distribution congestion, improved grid reliability and power quality, better energy and load management, ancillary services such as voltage stability and national security. Though the Distributed Generation has many advantages, it has variety of problems during grid integration. For example: protection of Distributed Generators [3, 4] when it is connected with the existing utility grid. These issues should be addressed effectively or else the reliability and the quality of electrical power supply will be poor. When connecting the inverter to the utility grid, either a pure inductor (L) or an LCL filter can be used as the inverter output stage. The LCL filter instead of L filter is more attractive because it cannot only provide higher high-frequency harmonic attenuation with the same inductance value but can also allow the inverter to operate in both stand-alone and grid-connected modes, which makes it a universal inverter for DG applications [8-11]. However, the system incorporating LCL filters is of third order, and it has an inherent high-resonant peak at the resonant frequency of the LCL filter, which will make the current control unstable if the controller is not suitably designed. To avoid this stability problem, the passive or active damping methods are usually used [1]. In [8], an admittance compensator along with a quasi-resonant-proportional controller was proposed. Using the inverter-output current instead of the grid current as the feedback signal, the control system can be simplified to a first order system, thus, it is possible to keep the control loop stable with high loop gain and bandwidth. However, from the whole system view, the filter capacitor and the grid-side inductor form a parallel resonant circuit, and harmonic current from inverter output in the vicinity of resonant frequency can be amplified excessively and may cause the resonance of the grid current. Reference [10] proposed a new control strategy with feedback of grid current plus part of the capacitor current. In this way, the inverter control system can also be degraded from third order to first order due to the counteraction between zeros and poles This proposed project analyses the stability problem of the grid connected Voltage Source Inverters with LC filters, which illustrates that the possible grid-impedance variations have a significant influence on the system stability. Whenever the grid inductive impedance increases, the low frequency gain and the bandwidth of the PI controller have to be decreased to maintain the system stable, thereby degrading the tracking performance and disturbance rejection capability. To overcome this problem an H∞ controller is proposed with explicit robustness in terms of grid impedance variations to incorporate the desired tracking performance and stability margin.
THREE-PHASE GRID-CONNECTED INVERTER USING CURRENT REGULATOR
This paper presents an approach for a three-phase grid-connected inverter using current regulator. The switching frequency of hystereris in the current modulation is fixed by comparing the current error with carrier wave with the constant frequency of the multiple of 3. The LCL filter is installed at the inverter output to offer high harmonic attenuation. In order to determine simply the parameters of PI regulators, the methods of PSO, GA and the conventional Ziegler-Nichols are used to search the best values with high global stability. The simulation results in Simulink/Matlab show that the PI regulators designed by PSO method demonstrate better results than Ziegler-Nichols and even GA technique.
International Journal of Electrical Power & Energy Systems, 2020
Variable voltage and current harmonics appear to be critical challenges for grid-connected inverters at the point of common coupling (PCC). The nonlinear local load and grid impedance variations contribute a lot to the problem. In this paper, a novel control strategy is proposed using the variable virtual admittance (VVA) and series active filter concepts capable of improving harmonic mitigation and stability in grid-connected inverters. The magnitude and phase angle of the VVA are adaptively determined according to the local load variation. Moreover, the series active filter injects a series voltage to reduce the grid impedance effect. The proposed control method can be simply implemented, where sinusoidal grid-injected current and sinusoidal local load voltage can also be achieved under local load variation and weak grid condition. The theoretical approach is verified using several simulation case studies in Matlab/Simulink software.
Comparative Study of DC/AC Inverter Control Techniques for Three Phase Grid Connected PV System
TEM Journal
The goal of this project is to develop and analyze a three-phase grid-connected photovoltaic (PV) system with a 250KW power capacity with expandable property. The PI, Slide, and MPC methodologies are used to test three distinct inverter current control techniques. The dynamic performances of the three inverter control techniques are virtually comparable under grid connected working conditions, although the dynamic performances of the traditional PI control technique are slightly better and smoother than the other two inverter control techniques. The unity power factor criterion was reached by all techniques. The output power levels obtained using the sliding mode inverter control method are higher than those obtained using the PI and MPC methods. MPC's DC link voltage readings are also consistent and match the intended voltage levels.
Investigation of Three-Phase Grid-Connected Inverter for Photovoltaic Application
This paper describes the investigation of the grid-connected three-phase inverter for photovoltaic (PV) application. The inverter control system modeling is carried out in MATLAB/SIMULINK environment. With the aids of the proportional-integral controllers, sinusoidal pulse-width modulation (SPWM) control technique and Park transformation, the inverter control system managed to convert PV power to ac power, stabilize the output voltage and current, and feeds the excess power to the utility grid. The control system generates the PWM signals for power devices, the insulated gate bipolar transistors in order to regulate the output voltage and current. In addition, the system is simulated with the PV simulator in order to facilitate the real PV power that to be fed to the input of the inverter. The control system produced 2.48% and 4.64% of output voltage and current total harmonic distortion, respectively. The simulation results such as the ac output voltages and currents, inverter system power flow, and grid disturbances detection signals, proved the effectiveness of the developed control algorithm. For the validation, this model is to be linked to the inverter prototype by utilizing the dSPACE controller.
High efficiency THIPWM three-phase inverter for grid connected system
2010 IEEE Symposium on Industrial Electronics and Applications, ISIEA 2010, 2010
This paper presents a grid connected system. Three phase DC-AC inverters used to convert the regulated DC power to AC power suitable for grid connection. Third harmonic injection PWM (THIPWM) was employed to reduce the total harmonic distortion and for maximum use of the voltage source. DSP was used to generate the accurate THIPWM for grid connection, by synchronizing the inverter voltage with the grid voltage. The application of THIPWM to parallel connected inverter reduces the total harmonic distortion and increases efficiency of the inverter. Experimental results validate the developed model and the proposed system. http://ieeexplore.ieee.org/xpls/abs\_all.jsp?arnumber=5679489&tag=1
RESEARCH AND DESIGN OF GRID-CONNECTED INVERTER IN PHOTOVOLTAIC SYSTEM WITH SVPWM TECHNIQUE
International Journal of Engineering Technologies and Management Research, 2019
This paper presents the design and simulation of three phase grid-connected inverter for photovoltaic systems with power ratings up to 5 kW. In this research, the application of Space Vector Pulse Width Modulation (SVPWM) technique for inverter is explored. With the use of SVPWM inverter, synchronization between the inverter and electrical grid follows the Phase-locked Loop (PLL) algorithm. The proposed design is simulated and validated by experimental results.
A Simple Current Control Strategy for Single-Stage Grid Connected Three-Phase PV Inverter
American Journal of Electrical and Electronic Engineering, 2016
This paper presents a new simple method of current control strategy of grid connected PV system. As the solar irradiation is a nonlinear quantity, so the connection of PV system with the grid is a difficult task. The objective of this work is to develop a model of the photovoltaic system with MPPT connected to 11KV grid by implementing new control technique so that maximum active power transfer from PV inverter to grid can be taken place without injection of harmonics. This paper also demonstrates the dynamic model of single-stage three-phase grid connected inverter. Here, for simplification the PV system is realized as a constant DC voltage source by using maximum power point tracking (MPPT) and boost converter. A current control strategy with pulse width modulation (PWM) technique is proposed to provide pulse for voltage-source inverter (VSI). The analysis and control design of grid connected PV inverter using PI control technique is done in synchronous d-q rotating reference fram...
SIMULATION AND COMPARISON OF SPWM AND SVPWM CONTROL FOR THREE PHASE INVERTER
A voltage source inverter is commonly used to supply a three-phase induction motor with variable frequency and variable voltage for variable speed applications. A suitable pulse width modulation (PWM) technique is employed to obtain the required output voltage in the line side of the inverter. The different methods for PWM generation can be broadly classified into Triangle comparison based PWM (TCPWM) and Space Vector based PWM (SVPWM). In TCPWM methods such as sine-triangle PWM, three phase reference modulating signals are compared against a common triangular carrier to generate the PWM signals for the three phases. In SVPWM methods, a revolving reference voltage vector is provided as voltage reference instead of three phase modulating waves. The magnitude and frequency of the fundamental component in the line side are controlled by the magnitude and frequency, respectively, of the reference vector. The highest possible peak phase fundamental is very less in sine triangle PWM when compared with space vector PWM. Space Vector Modulation (SVM) Technique has become the important PWM technique for three phase Voltage Source Inverters for the control of AC Induction, Brushless DC, Switched Reluctance and Permanent Magnet Synchronous Motors. The study of space vector modulation technique reveals that space vector modulation technique utilizes DC bus voltage more efficiently and generates less harmonic distortion when compared with Sinusoidal PWM (SPWM) technique. In this paper first a model for Space vector PWM is made and simulated using MATLAB/SIMULINK software and its performance is compared with Sinusoidal PWM. The simulation study reveals that Space vector PWM utilizes dc bus voltage more effectively and generates less THD when compared with sine PWM.