Three-phase PV Inverter Research Articles

Three-Phase Transformerless PV Inverter With Reconfigurable LCL Filter and Reactive Power Capability

Three-Phase Transformerless PV Inverter With Reconfigurable <i>LCL</i> Filter and Reactive Power Capability

Innovative approaches for minimizing leakage current in three-phase transformerless PV inverters

Innovative approaches for minimizing leakage current in three-phase transformerless PV inverters

A Control Strategy for Two-stage PV Grid-connected Inverter Based on Voltage Oriented Control

For the design of three-phase two-stage grid-connected PV inverter, the topology and control strategy of two-stage grid-connected inverter are analyzed. For the DC/DC converter control strategy, the shortcoming of conventional perturbation and observation method are analyzed, which is difficult to obtain high response speed and steady-state tracking accuracy due to its fixed disturbance step size. A duty cycle self-optimizing MPPT method is adopted and effectively alleviates the contradiction between tracking speed and accuracy. For the DC/AC converter control strategy, the grid voltage oriented vector control is adopted based on the analysis of the mathematical model of rotating coordinate. The current decoupling and grid voltage feedforward control in dq coordinate system are carried out. The control system parameters are designed and verified to be feasible.

Adaptive dc-link voltage control strategy to increase PV inverter lifetime

This work proposes an adaptive dc-link voltage strategy applied to a double-stage three-phase grid-connected PV inverter, in order to decrease the power devices and capacitors thermal stress, and increase the system-level reliability as a consequence. The objective is to reduce the dc-link voltage to the minimum value required to inject power into the grid. A system reliability analysis is made based on mission profiles from Brazil. The results show that the proposed technique has a positive impact on the system reliability, increasing the estimated lifetime by 75% when compared to the traditional fixed dc-link voltage strategy.

Operation of a Transformerless Three-phase PV Inverter Using Multiple Bidirectional Choppers

Operation of a Transformerless Three-phase PV Inverter Using Multiple Bidirectional Choppers

Lifetime evaluation of three-phase multifunctional PV inverters with reactive power compensation

The multifunctional operation of photovoltaic inverters consists in providing ancillary services to the grid, such as reactive power injection, harmonic current compensation, frequency regulation and others. These extra activities can cause higher electro-thermo-mechanical stress in the inverter components, affecting their reliability. Hence, this work aims to analyze the multifunctional inverters reliability when the injection of a real industry reactive power profile is performed. The evaluation has been carried out on a grid-connected three phase photovoltaic system, considering a mission profile from Denmark. An equivalent thermal model is used to estimate the power devices junction temperature. Furthermore, a lifetime model applied to the Palmgren-Miner's rule is used to evaluate the inverter lifetime consumption. Afterward, a statistical analysis simulates several power devices operation scenarios, for the cases with and without reactive power injection. Finally, the results show that the reactive power injection has a considerable impact on the inverter reliability, reducing by 3 and 1.5 times the lifetime estimation when this service is performed without power restrictions and considering the dynamic power saturation, respectively.

Model Predictive Voltage Control Based on Finite Control Set With Computation Time Delay Compensation for PV Systems

For the conservativeness and computational delay of the traditional finite control set model predictive control (FCS-MPC), a multi-step model predictive voltage control method based on finite control set (FCS-MMPVC) with delay compensation method is proposed in this paper, and the proposed method is validated on a three-level three-phase voltage source PV inverter. In each control cycle, the 27 voltage vectors for inverters are evaluated on line based on predictive model to obtain the optimal and suboptimal switching state. The selected switching state is optimal in two control cycle with the proposed method. Considering that the time spent in the actual sampling and calculation process cannot be ignored, the delay compensation is added in FCS-MMPVC algorithm. The simulation and experimental results show that the proposed method has good stability and reliability. Compared with the traditional FCS-MPC algorithm, the proposed method can reduce the difference significantly between the output voltage and the reference under the unbalanced and non-linear load, and the output voltage quality of the inverter is improved.

A Single-Stage Soft-Switching High-Frequency AC-Link PV Inverter: Design, Analysis, and Evaluation of Si-Based and SiC-Based Prototypes

This paper proposes a high-power-density and reliable inverter topology, which transfers the maximum power of a PV array to the load in one power conversion stage. The single-stage power conversion, along with the soft-switching capability of the proposed three-phase PV inverter promises high efficiency at all operating points. Instead of a capacitive dc link that decouples the dc–dc converter and the voltage source inverter in traditional two-stage PV inverters, a high-frequency capacitive ac link is employed in the proposed inverter, which enables exploiting a very small film capacitor, rather than a bulky electrolytic capacitor, for transferring power. Eliminating electrolytic capacitors prolongs the lifetime of this inverter. Considering the long lifetime of PV modules, this feature is of high importance in PV applications. The high-frequency ac link also allows using high-frequency transformers for providing galvanic isolation. Therefore, this inverter is expected to have a very high power density. This paper presents principles of the operation and control, design, and analysis of this inverter, and verifies the performance of the inverter through two prototypes: a 2-kW Si-based prototype and a 2-kW SiC-based prototype operating at different switching frequencies.

Improving the Performance of Low Voltage Networks by an Optimized Unbalance Operation of Three-Phase Distributed Generators

This work focuses on using the full potential of PV inverters in order to improve the efficiency of low voltage networks. More specifically, the independent per-phase control capability of PV three-phase four-wire inverters, which are able to inject different active and reactive powers in each phase, in order to reduce the system phase unbalance is considered. This new operational procedure is analyzed by raising an optimization problem which uses a very accurate modelling of European low voltage networks. The paper includes a comprehensive quantitative comparison of the proposed strategy with two state-of-the-art methodologies to highlight the obtained benefits. The achieved results evidence that the proposed independent per-phase control of three-phase PV inverters improves considerably the network performance contributing to increase the penetration of renewable energy sources.

Flexible harmonic current compensation strategy applied in single and three-phase photovoltaic inverters

Non-linear loads connected to power system have increased considerably in the recent decades. Traditional generation based on hydro and thermal power plants cannot mitigate harmonic currents. However, due to the increased connection of photovoltaic into the power system, its power electronic converter can be used to perform ancillary services such as harmonic current compensation. This work presents a dynamic method based on the Second Order Generalized Integrator coupled with a phase locked loop structure to detect and compensate the most predominant harmonic current components from the power system. It is also presented an extension to detect multiple harmonics, according to the amplitude. Technical issues related with the harmonic current compensation strategy, and its implementation for both single and three-phase PV inverters are explored to demonstrate the functionality and efficiency of the method. The results show the harmonic current compensation being compensated by a PV inverter. Finally, a losses analysis were performed in the LCL filter. The magnetic and damping resistor losses are more impacted due to high harmonic current compensation.

Design of A Grid Integrated PV System with MPPT Control and Voltage Oriented Controller using MATLAB/PLECES

This paper presents model of a grid-integrated photovoltaic array with Maximum Power Point Tracker (MPPT) and voltage oriented controller. The MPPT of the PV array is usually an essential part of PV system as MPPT helps the operating point of the solar array to align its maximum power point. In this model, the MPPT along with a DC-DC converter lets a PV generator to produce continuous power, despite of the measurement conditions. The neutral-point-clamped converter (NPC) with a boost converter raises the voltage from the panels to the DC-link. An LCL-filter smoothens the current ripple caused by the PWM modulation of the grid-side inverter. In addition to the MPPT, the system has two more two controllers, such as voltage controller and a current controller. The voltage control has a PI controller to regulate the PV voltage to optimal level by controlling the amount of current injected into the boost stage. Here, the grid-side converter transfers the power from the DC-link into the grid and maintains the DC-link voltage. Three-phase PV inverters are used for off-grid or designed to create utility frequency AC. The PV system can be connected in series or parallel to get the desired output power. To justify the working of this model, the grid-integrated PV system has been designed in MATLAB/PLECS. The simulation shows the P-V curve of implemented PV Array consisting 4 X 20 modules, reactive, real power, grid voltage and current.

Adaptive Harmonic Elimination in a Grid-Connected Three-Phase PV Inverter

Adaptive Harmonic Elimination in a Grid-Connected Three-Phase PV Inverter

Direct power control of a grid-connected photovoltaic system using a fuzzy-logic based controller

In this paper a fuzzy logic-based controller is proposed for direct power control of three-phase grid-connected photovoltaic PV inverters. To demonstrate the effectiveness of the control method, a typical grid-connected PV inverter is implemented and the performance of the proposed technique is compared to a traditional proportional-integral PI controller. Numerical simulation results illustrate that the proposed fuzzy controller performs well in independently regulating the active and reactive output powers. Moreover, comparisons of simulation results between fuzzy and PI controllers show advantages of the fuzzy-based technique in terms of transient response characteristics, such as fast response, small overshoot, acceptable steady-state fluctuation, and high robustness.

A Simple Current Control Strategy for Single-Stage Grid Connected Three-Phase PV Inverter

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 frame to achieve maximum output voltage response and active power. The considered system consists of a VSI, 3-Φ filter, a control system, a distribution network, load and grid. As PV inverter should inject only active power, so reactive power injected to the grid is made zero with the help of this control technique. There after the final model is simulated by using MATLAB/SIMULINK and different output waveforms are analyzed for three different conditions.

The Generation of Three-Phase SPWM Wave Based on FPGA

This paper presents a method of generating the three-phase SPWM wave based on FPGA. In a three-phase PV inverters or other using DC to converte into a three-phase AC system,it can be used as six IGBT gate drive signals of a three-phase inverter bridge.This article analysed the principle of the three-phase inverter circuit , obtaining the waveform of the three-phase SPWM wave. The 60 SPWM wave of each sine wave at 50Hz,it designs the hardware circuit to generate the waveform. Hardware circuit of hardware programming language makes the simulation of the three-phase drive waveform in Quartus II,and the program is downloaded into FPGA chip Cyclone II EP2C8Q208N to get waveform output. This design uses a counter method, checking ROM table to determine the preset value of the counter, and the output pulse width control can be achieved by changing the size of the preset value. We designes a three-phase adjustable power using this method and achieved the intended purpose.

Fault Diagnosis and Fault-Tolerant Control of DC-link Voltage Sensor for Two-stage Three-Phase Grid-Connected PV Inverters

This paper proposes a method for fault diagnosis and fault-tolerant control of DC-link voltage sensor for two-stage three-phase grid-connected PV inverters. Generally, the front-end DC-DC boost converter tracks the maximum power point (MPP) of PV array and the rear-end DC-AC inverter is used to generate a sinusoidal output current and keep the DC-link voltage constant. In this system, a sensor is essential for power conversion. A sensor fault is detected when there is an error between the sensed and estimated values, which are obtained from a DC-link voltage sensorless algorithm. Fault- tolerant control is achieved by using the estimated values. A deadbeat current controller is used to meet the dynamic characteristic of the proposed algorithm. The proposed algorithm is validated by simulation and experiment results.