This paper presents an adaptive proportional resonant (PR) controller for single phase grid connected inverter that adapts its control parameters to grid impedance variations. Forth order band bass filter is designed and then integrated with the adaptive scheme for on-line detection of any variations in the resonance frequency. The estimated frequency is then processed by statistical signal processing operation to identify the variations in the grid impedance. For the on–line tuning of the PR parameters, a look-up table technique is utilized and its parameters are linked with the estimated impedance values. Simulation results based on MATLAB environment clearly verify the effectiveness of the proposed control scheme for 2 kW grid connected inverter system.
1. Adaptive Proportional Resonant Controller
2. Grid Impedance Estimation
3. LCL Filter
4. Look-up Table
Fig. 1. Block diagram of the proposed adaptive PR controller.
EXPECTED SIMULATION RESULTS:
Fig. 2. Simulation result of emulated grid voltage.
Fig.3. FFT analysis of grid current. (a) APR controller. (b).PR controller.
Fig. 4. Online adaptation of the APR control parameters.
Fig. 5. Grid voltage and current waveforms under changeable grid
impedance with the proposed control strategy.
A new control strategy based on an adaptive proportional resonant (APR) controller has been developed and successfully tested on a simulated 2 kW single phase grid tide PV inverter. A fourth order Sallen-Key bandpass filter tailored to the system to capture the harmonic components around the resonant frequency has been implemented. Statistic signal processing technique was employed in order to provide the controller with signals corresponded to the changeable grid impedance. A considerable low level of current total harmonic distortion (THD) is achieved in comparison with conventional PR controller and compliance with IEEE929-Standard has been demonstrated.
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