PROJECT TITLE :
A Real-Time Computation Method With Dual Sampling Mode to Improve the Current Control Performance of the $LCL$-Type Grid-Connected Inverter
Because of the upper attenuation of switching frequency current harmonics, the $LCL$ filter has been widely employed in grid-connected inverters. To cater to the resonance of the $LCL$ filter, the capacitor current is sometimes fed back to damp the resonance actively. But, the computation and pulsewidth modulation (PWM) delays within the digital control system have a important influence on the active damping method, ensuing in poor system robustness. Meanwhile, these delays additionally reduce the management bandwidth greatly and so impose a severe limitation on the low-frequency gains. During this paper, a real-time computation method with twin sampling mode is proposed to get rid of the computation delay from the inner active damping loop and therefore the outer grid-current management loop simultaneously; therefore, the system robustness and therefore the management performance will be greatly improved. Moreover, the time length between the sampling instant and the switching transition of the inverter bridge is extended by the proposed method, which effectively prevents the switching noise distorting the sampled signals. Thus, the noise immunity of the inverter is also improved greatly. Experimental results from a six-kW $LCL$-type single-phase grid-connected inverter confirm the theoretical expectations and also the effectiveness of the proposed technique.
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