Control Of Photovoltaic Grid-connected Inverter Research Articles

Current PIλ Control of the Single-Phase Grid Inverter

In a grid-connected power generation system, the grid-connected current of the inverter is sensitive to nonlinear factors such as periodic disturbance of grid voltage, which results in grid-connected current waveform distortion. By establishing a single-phase photovoltaic grid-connected inverter control system model, designing an inverse current fractional-order PI (PIλ or FO-PI) controller and the dynamic and steady-state performance, antidisturbance and grid connection inversion characteristics of the system are simulated and compared under the action of the integer-order PI controller and fractional-order PI controller. The quality of the inverter grid-connected current is analyzed by using the fast Fourier transform (FFT). The simulation results show that the fractional-order control system can reduce the total harmonic distortion (THD) of the grid-connected current and dynamic performance and antidisturbance ability of the improving system while satisfying the steady-state performance indexes.

Frequency conversion control of photovoltaic grid-connected inverter based on LCL filtering

Abstract Aiming at the problem that the filtering effect of inductor capacitance inductor (LCL) filter becomes worse when the Photovoltaic (PV) system works at low power, this paper presents a control strategy to change the switching frequency according to the instantaneous output power of the inverter. By analyzing the design method of each parameter of LCL filter, a single-stage PV grid-connected inverter structure is used to establish the frequency loop based on grid voltage-oriented vector control to determine the optimal switching frequency under the current power state. The design methods of power detector, frequency calculation and frequency hysteresis comparator are analyzed in detail. Finally, the waveforms of grid-connected current before and after frequency conversion are contrasted by MATLAB simulation to verify the feasibility and effectiveness of the inverter control strategy.

Single-phase photovoltaic grid-connected inverter for predictive control method with power feed-forward

In the traditional photovoltaic grid-connected inverter control, there are problems such as slow system response speed, low stability and grid-connected current distortion. In this regard, a novel current prediction control method for grid-connected inverter with power feed-forward is proposed. The method consists of DC voltage outer loop control, current predictive control, power feed-forward and grid voltage feed-forward. The characteristic is that the current prediction control algorithm derived from the state equation of the grid-connected inverter effectively suppresses the influence of DC voltage fluctuation on the grid-connected current and enhances the robustness of the system; the introduction of power feed-forward accelerates the dynamic response of the system; The introduction of grid voltage feed-forward reduces voltage distortion or current distortion. And the traditional PI control module is not needed, the structure is simple, and the circuit is easy to implement. Matlab/Simulink simulation model and experimental results prove the effectiveness of the proposed control method, which is more practical than the traditional double loop control method.

Discrete-Time Optimal Control of Photovoltaic Grid-Connected Inverter Based on Particle Swarm Optimization

This paper is concerned with the problem of optimal control of photovoltaic grid-connected inverter. Firstly, the discrete-time nonlinear mathematical model of single-phase photovoltaic grid-connected inverter in the rotating coordinate system is constructed by the Delta operator, which simplifies the control process and facilitates direct digital realization. Then, a novel optimal control method which is significant to achieve trajectory tracking for photovoltaic grid-connected inverter is developed by constructing a control Lyapunov functional against the difficulty of solving HJB (Hamilton-Jacobi-Bellman) partial differential equations. More importantly, the performance matrix of the controller which is very meaningful to many performance indicators of the system is also optimized via the particle swarm optimization. Finally, two numerical examples are provided to illustrate the effectiveness of the proposed method.

The Research of Two Staged Non-Isolated Photovoltaic Grid Connected Inverter Control Method

Grid-connected inverter topologies and control methods are analyzed and compared on the basis of two non-isolated PV grid-connected inverter circuit topology as 3kVA grid connected PV systems. In this paper, the current control method, the DC bus voltage outer grid current inner loop of the dual closed-loop PI control method. Sampled signal through the system circuit for processing, resulting in a SPWM drive signal to control the conduction of the power devices off the grid current control.

Analysis of the Deadbeat Control Algorithm for Photovoltaic Grid Connected Inverter Output Current

Photovoltaic grid connected inverter is the core interface device in the photovoltaic power generation system to grid. The power quality of photovoltaic power generation system is affect by the waveform of output sinusoidal AC current directly. In this paper, current deadbeat control algorithm and a two-stage photovoltaic grid-connected inverter control strategy are proposed by analyzing the derivation of a photovoltaic grid-connected inverter. According to the grid connected Photovoltaic system features, a set of three-phase Photovoltaic grid connected inverter is designed, which rated power is 15 kW. The deadbeat control algorithm is introduced, based on the analysis of photovoltaic grid connected inverter topology, grid connected voltage, current, power, and the current waveform distortion rate. The deadbeat control algorithm is effective to control the three phase inverter output current through the system simulation and analysis.

Research on Current Control of Photovoltaic Grid-Connected Inverter

Grid-voltage feed-forward control was added to improve the grid-connected current quality on photovoltaic grid-connected inverter. The method decreases the phase difference between the grid-connected current and grid voltage and reduces the total harmonics distortion (THD) of grid-connected current. So the grid-voltage feed-forward compensation can improve grid-connected current availably and keep the current frequency and phase synchronous to the grid. The study is validated through simulations and field experiments. Experimental results obtained on 2.5-kw inverter demonstrate the feasibility of the proposed method.

Passivity–Based Control of Photovoltaic Grid-Connected Inverter

Photovoltaic (PV) grid-connected system requires the inverter possesses excellent dynamic and static characteristics. In the view of the mathematical model of the inverter is nonlinear, we will adopt a kind of nonlinear control strategy called Passivity–Based Control (PBC). First we establish the standard Euler – Lagrange (EL) mode for inverter, then we also prove that this inverter is strictly passive. Based on passivity of inverter, we can redistribute the system energy, and adopt the approaches of injecting damping and decoupling to improve system performance. In this paper, we can control the active and reactive power of system to make system can fast track the PV array maximum power point, and possess the capacity of compensating the reactive power. Simulation results show that passivity-based control method can make the inverter possess better robustness and dynamic.

Model Predictive Control Based on System Identificationof Photovoltaic Grid Connected Inverter

This paper proposes a model predictive control of photovoltaic grid-connected inverter based on system identification. The single phase inverter is experimented and its model is determined by using System identification approach with Hammerstein-Wiener model. The derived nonlinear voltage model has accuracy more around 97.34% and it is transformed to the state space model by linearization. A simulation of model based controller uses the discrete time model of inverter to predict the behavior of the output voltage for each possible switching state every sampling time. Then cost function is applied as a criterion for selecting the most suitable switching state for the next sampling interval. The model output is compared with the reference voltage sine wave and the error is feedback to the optimizer. Simulation results shown that the proposed control scheme can achieve the output target with 97% of accuracy.