Single-phase Grid-connected PV Inverter Research Articles

A study of a single phase grid connected pv inverter performance under a weak grid conditions and distorted grid voltage for Cambodia

<span lang="EN-US">A single-phase grid-connected PV inverter performance under a weak grid is a model designed to penetrate PV energy with a weak grid. Usually, this model gets complex and unstable in power system control such as THD growth, harmonic effects, voltage surges, inverter performance. Experimental results would present the impacts on the system which would lead to instability in the grid system. This study was based on inverter performance control, a weak grid control, the grid distortion examination, and harmonic effects. To optimize this grid system, hence, the proposed methods of oscilloscope and power meter were proportionally used to control the grid impacts and stabilities. The results showed that current THD in distorted grid voltage system surged to 8.88%. V<sub>PCC</sub> growth was 238.11V, equivalent to 8.23% in a weak grid (X<sub>L</sub> and R). Such a huge increase could prevent the grid system from transferring power for later operation. During the experiment, the inverter, S power and Q power performances stood for good operating processes without impacts on the grid performance. This method should be applied with a weak grid system because it provided information about grid stability control.</span>

Design of type-1 servo controller for grid voltage modulated direct-power control of single-phase grid-connected PV inverter

This paper presents direct control of active and reactive power using grid voltage modulation for single-phase grid-connected photovoltaic inverter. A design of type-1 servo system based on pole-placement method is proposed to control the power flow using a simplified multiple-input multiple-output (MIMO) model of the system. Phase-locked loop (PLL) with a quarter cycle time delay is used to estimate the grid phase angle for the purpose of performing the stationary and synchronous reference frame transformation. Unipolar pulse width modulation (PWM) technique is used to control a single-phase inverter with 2.7 KVA capacity connected to the photovoltaic system. The proposed controller can simply be tuned using minimum number of controller gains to achieve the transient and steady-state performance requirements. The proposed system, was capable of operating for a wide range of solar irradiance levels with a power factor in the range of 0.95 (leading/lagging), for the reactive power compensation purposes.

Symmetrical Pole Placement Method-Based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller With Harmonic Compensator for Single Phase Grid-Connected PV Inverters

In this paper, a symmetrical pole placement Method-based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller is presented. The proposed PR-P controller resolved the issues that are tracking repeating control input signal with zero steady-state and mitigating of 3rd order harmonic component injected into the grid associated with the use of PI controller for single-phase PV systems. Additionally, the PR-P controller has overcome the drawbacks of frequency detuning in the grid and increase in the magnitude of odd number harmonics in the system that constitute the common concerns in the implementation of conventional PR controller developed as an alternative to PI controller. Moreover, the application of an unprecedented design process based on changing notch filter dynamics with symmetrical pole placement around resonant frequency overcomes the limitations that are essentially complexity and dependency on the precisely modelled system associated with the use of various controllers such as Adaptive, Predictive and Hysteresis in grid connected PV power generation systems. The proposed PR-P controller was validated employing Photovoltaic emulator (PVE) consisting of a DC-DC Buck power converter, a maximum power point tracking (MPPT) algorithm and a full-bridge grid connected inverter designed using MATLAB/Simulink system platform. Details of the proposed controller, Photovoltaic emulator (PVE) simulations, analysis and test results were presented in the paper.

Adaptive-Harmonic Compensation in Residential Distribution Grid by Roof-Top PV Systems

The single-phase nonlinear loads are going to increase in the future and power quality concerns in the residential distribution grid. Since most of nonlinear loads have a dispersed nature, compensating these phenomena may be complicated. On the other hand, the increased capacity of single-phase grid-connected roof-top PV inverters in residential distribution grid can be an opportunity to engage these systems in the power quality issues as custom power devices. By implementing a proper control for roof-top PV inverters, these systems may in addition to inject the fundamental current, additionally act like a virtual harmonic resistance, and dedicate their additional current capacity to compensate the harmonics of residential distribution grid. In this paper, each roof-top PV system is a grid-harmonic supervisor, where it continually measures the PCC voltage harmonics by the sliding discrete Fourier transform algorithm and then individually compensates the measured harmonics by the proposed adaptive-harmonic compensator. In the proposed approach, a current reference is separately determined for compensating each harmonic component. Then, a specific amount of additional current capacity will be dedicated for each component to compensate by using adaptive gain. Finally, the current reference is controlled by a model predictive current controller. It has been tested in a single-phase transformerless inverter (highly efficient and reliable inverter concept) with an LCL filter at the output. Also, the effectiveness of the control scheme has been verified by MATLAB Simulink and experimental tests.

The Partial Linearization of Power-Voltage Curve for Grid-Connected Photovoltaic System

This paper aims to present a new method to track the maximum power point for single-stage single-phase grid connected PV inverter, which is based on the partial linearization of the power-voltage PV panel curve coupled to the MPPT algorithm. The proposed approach generates the reference current in order to regulate the power fed into the grid, and it needn’tany accuracy of the PV panel model which may change over time. The current controller approach is based on the stability of the internal dynamic due to the nonlinearity of the PV system and it uses the Lyapunov function that gives globally asymptotically stable trajectories of the closed-loop system. The effectiveness of the control algorithm has been verified by simulating it in Matlab/Simulink software. The proposed control is compared with the conventional approach using PI controller.

A Systematic Method for Designing a PR Controller and Active Damping of the LCL Filter for Single-Phase Grid-Connected PV Inverters

The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors and limited disturbance rejection capability. Compared with the L- and LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. Therefore, damping must be introduced to improve the control of the system. Considering the controller and the LCL filter active damping as a whole system makes the controller design method more complex. In fact, their frequency responses may affect each other. The traditional trial-and-error procedure is too time-consuming and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter regarded as a whole system. In addition, the paper presents a systematic method for designing controller parameters and the capacitor current feedback coefficient factor of LCL filter active-damping. The new method relies on meeting the stable margins of the system. Moreover, the paper also clarifies the impact of the grid on the inverter output current. Numerical simulation and a 3 kW laboratory setup assessed the feasibility and effectiveness of the proposed method.

The Output Current Controller of a Single-phase Grid-connected PV Inverter in Discrete Fourier Transform

The output current of grid-connected PV inverters should not excess harmonic contents. Also, because they are driven connected with grid, the reliability of electric power’s quality should be secured. But, the current controllers of the grid-connected PV inverter decrease the electric power’s quality due to not considering the harmonic contents of the output current. This paper proposed the current controllers of the grid-connected PV inverters to supplement the decrease of the electric power’s quality because of the harmonic contents of the electric power’s quality and the harmonic contents of the output current. The proposed current controllers controlled the harmonic contents of the output current by controlling gains of the current controllers in consideration of the harmonic contents of the output current. As a result, when total harmonic distributions of the grid voltage were 0.4% and 4.1%, the excellence of the proposed current controllers was shown through the experience, by obtaining excellent results of being controlled low as the total harmonic distributions of the output current were 0.756% and 0.78% respectively.