A Control Parameters Design Method With Multi-Constrains for an LCL-Filtered Grid-Connected Inverter in a Weak Grid

Under weak grid conditions, the variation of the grid impedance will affect the steady-state and dynamic performance of the LCL-filtered grid-connected inverter and even make the inverter unstable. To ensure the system stability and further improve the dynamic performance in a weak grid, a control parameter design method with multi-constrains considering the system bandwidth for the current controller and active damping is proposed in this paper. First, based on the current controller and active damping with only grid current feedback, the effects of control parameters and grid impedance on the LCL resonant suppression and the performance of the inverter are analyzed. Moreover, the parameter constraints of the controllers are derived considering the grid impedance, including stability, resonance suppression, and margin constraints. Furthermore, as the system bandwidth affects the dynamic performance of the inverter, combined with the obtained multi-constraints, the optimal control parameters are determined by achieving the maximum bandwidth of the system against the impedance variation. Compared with other two methods, when the proposed method is applied, the system can operate with a better dynamic and steady-state performance. Finally, experiments are performed on a 2 kW three-phase grid-connected inverter in the weak grid, which verify the effectiveness of the parameter design method proposed in this paper.

Operation and Startup of Three-Phase Grid-Connected PWM Inverter for an Experimental Test Bench With DSPACE Real-Time Implementation of PQ Control

The main objective of this chapter is the experimental validation of active and reactive power control at the connection point for a three-phase grid connected inverter. It gives an overview on the adopted vector control strategy, regulation of the angle of orientation of the blades (pitch control), synchronization grid side converter to the power network using phase closed loop (PLL). Once the experimental test bench is described, the authors devote a first part to the design of the block circuit diagram of the experimental platform and the control strategy implemented in the DSPace DS1104, and they suggest some steps to associate the inverter to the electrical network. Subsequently, they discuss the experimental results validating the proposed power control. The purpose of this experimental results is the DSPACE real-time implementation of PQ control using three-phase inverter and development of a startup algorithm of the experimental test bench.

Grid-Connected Inverter for a PV-Powered Electric Vehicle Charging Station to Enhance the Stability of a Microgrid

This study proposes a grid-connected inverter for photovoltaic (PV)-powered electric vehicle (EV) charging stations. The significant function of the proposed inverter is to enhance the stability of a microgrid. The proposed inverter can stabilize its grid voltage and frequency by supplying or absorbing active or reactive power to or from a microgrid using EVs and PV generation. Moreover, the proposed inverter can automatically detect an abnormal condition of the grid, such as a blackout, and operate in the islanding mode, which can provide continuous power to local loads using EV vehicle-to-grid service and PV generation. These inverter functions can satisfy the requirements of the grid codes, such as IEEE Standard 1547–2018 and UL 1741 SA. In addition, the proposed inverter can not only enhance the microgrid stability but also charge EVs in an appropriate mode according to the condition of the PV array and EVs. The proposed inverter was verified through experimental results with four scenarios in a lab-scale testbed. These four scenarios include grid normal conditions, grid voltage fluctuations, grid frequency fluctuations, and a power blackout. The experimental results demonstrated that the proposed inverter could enhance the microgrid stability against grid abnormal conditions, fluctuations of grid frequency and voltage, and charge EVs in an appropriate mode.

Analysis of Stationary- and Synchronous-Reference Frames for Three-Phase Three-Wire Grid-Connected Converter AC Current Regulators

The current state of the art shows that unbalance and distortion on the voltage waveforms at the terminals of a grid-connected inverter disturb its output currents. This paper compares AC linear current regulators for three-phase three-wire voltage source converters with three different reference frames, namely: (1) natural (abc), (2) orthogonal stationary (αβ), and (3) orthogonal synchronous (dq). The quantitative comparison analysis is based on mathematical models of grid disturbances using the impedance-based analysis, the computational effort assessment, as well as the steady-state and transient performance evaluation based on experimental results. The control scheme devised in the dq-frame has the highest computational effort and inferior performance under negative-sequence voltage disturbances, whereas it shows superior performance under positive-sequence voltages among the reference frames evaluated. In contrast, the stationary natural frame abc has the lowest computational effort due to its straightforward implementation, with similar results in terms of steady-state and transient behavior. The αβ-frame is an intermediate solution in terms of computational cost.

Composite Control Strategy of Output Current of LCL Photovoltaic Grid-Connected Inverter

In order to further optimize the output current harmonic suppression effect of photovoltaic grid-connected inverters, a composite control strategy of LCL type photovoltaic grid-connected inverter output current is proposed. This strategy combines proportional complex integral (PCI) control and repetitive control (RC) in parallel, draws a composite control block diagram, introduces a transfer function, and designs PCI and RC control parameters. Prove that the compound control can reduce current harmonics, achieved the purpose of reducing the steady-state error of the fundamental frequency. And adopts a new PCI composite control strategy, which helps to save the cost of the control system. By building the MATLAB/Simulink simulation platform and establishing the PCI+RC composite control model of LCL photovoltaic grid-connected inverter, the comparison of the simulation results shows that compared with the PI+RC control strategy, the total harmonic distortion rate of the grid-connected current is reduced by 25.77. %, significantly improving the quality of grid-connected current.

Allocation Control of Multi-functional Grid Connected Inverter and the Power Quality between of Grid Connected Microgrid Based on PSCAD Simulation Platform

On the one hand, the application of microgrid can effectively cut down the effect of distributed generation on distribution network, on the other hand, it helps to improve the power quality of distribution network. However, for the distribution network, a single multi-functional inverter has limited effect on the improvement of its power quality. Therefore, the allocation control of power quality by decentralized multi-functional inverters can further improve the utilization of inverters. This paper proposes to calculate the output current of multiple multi-functional inverters according to the harmonic and reactive current of the parallel node and the residual capacity of the multi-functional inverter. The simulation results show that the allocation control strategy proposed in this paper can effectively control the compensation capacity of the multi-functional inverter, so as to control the harmonic at the grid connection in place.