Abstract
In order to reduce the total harmonic distortion (THD) of the grid-connected current caused by the high-frequency switching of the inverter, this paper combines the high efficiency single-phase H6-type inverter with LCL filter. The double closed-loop control method that consists of grid-connected current outer loop and capacitor current inner loop is put forward, by which a resonance peak of a low damping LCL filter is eliminated. In the grid-connected current outer loop, quasi proportion resonant (QPR) controller is adopted to overcome the steady-state error and weak anti-jamming capability in traditional PI controller. Finally, a simulation model is built in SIMULINK to verify the research. The simulation results show that, based on the single-phase H6-type inverter and LCL filter, the double closed-loop QPR control strategy can achieve the static error free tracking control of grid-connected current, which makes the system more stable and reduces the THD of grid-connected current effectively.
Highlights
With the development of new energy industry and smart micro-grid, inverters have drawn more and more attention as the core of grid-connected system
Comparing the reference current iref with the grid-connected current i2, the obtained error signal is sent into the quasi proportion resonant (QPR) controller, the signal is compared with the capacitor current in the inner loop
Aimed at the problem that the oscillation of the third-order LCL filter causes the instability of the system, an active damping control scheme is adopted in this paper
Summary
With the development of new energy industry and smart micro-grid, inverters have drawn more and more attention as the core of grid-connected system. The PR controller solves the static error that can’t be eliminated by the traditional PI controller, and restrains the disturbance caused by the voltage of the power grid. In order to reduce the influence of high-frequency switching harmonics current on grid-connected current, the traditional grid- connected inverter is usually connected to the power grid with an L filter. Some methods are put forward these years (Zhuang C. et al, 2015; Sun W. et al, 2008) Those methods either need compensation control or cause new wastage, and these inverter topologies are ordinary H4-type inverters. As for the more efficient single-phase H6-type inverter, there are a few studies on using LCL filter for grid-connected inverter. In order to solve the above problems, this paper first analyzes the topology of a single-phase H6-type grid-connected inverter with LCL filter (H6LCL for short).
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