Control Strategy For Grid-connected Inverter Research Articles

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.

An Improved Repetitive Control Scheme for Grid-Connected Inverter With Frequency-Adaptive Capability

The power quality of grid-connected inverters has drawn a lot of attention with the increased application of distributed power generation systems. The repetitive control technique is widely adopted in these systems, due to its excellent tracking performance and low output total harmonic distortion (THD). However, in an actual system, the ratio of the sampling frequency to the grid frequency cannot always maintain an integer, and then, the resonant frequencies of the repetitive control technique will deviate from the real grid fundamental and harmonic frequencies. This will degrade the performance of the system, particularly when the grid frequency varies. Even if the ratio is a fixed integer, the auxiliary function for stabilization in the conventional repetitive control technique will also increase the steady-state tracking error and THD of the system. In this paper, an improved repetitive control scheme with a special designed finite impulse response (FIR) filter is proposed. The FIR filter cascaded with a traditional delay function can approximate the ideal repetitive control function of any ratio. The proposed scheme varies the FIR filter according to varied grid frequency and maintains its resonant frequencies matching the grid fundamental and harmonic ones. Finally, the simulation and experimental results show that the improved repetitive control scheme can effectively reduce the tracking error and compensate harmonics of the inverter systems.

Dual-loop Control Strategy for Grid-connected Inverter with LCL Filter

As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, damping resistance was virtualized, mathematical model under the DQ frame that can realize decoupling control was established, a dual-loop control strategy for grid-connected inverter with LCL filter was proposed, the system stability was analyzed and the design method of controller was given. The proposed method overcame the flaws of loss increase, efficiency reduce and cost increase which were caused by damping resistance in LCL type grid-connected inverter, the system efficiency and power supply quality of the output were improved. Feasibility and effectiveness of the new method were validated by simulation and experimental results.