Detection method for multi-harmonic current compensation applied in three-phase photovoltaic inverters

The new generation of PV systems can have the capability to perform ancillary services in order to improve the power grid quality index. One of these services is the harmonic current compensation of nonlinear loads. An important issue to perform this service is the harmonic detection method. The traditional methods detects all harmonic contents of the load current and the control tuning tends to be complex and few flexible, especially if it is used resonant controllers, once the load harmonic contents are not well defined. Therefore, in the literature is proposed a detection method of the harmonic load current, which is frequency adaptive and able to detect the load harmonic current of higher amplitude. This method consists in two stages of second order generalized integrator structure with synchronous reference frame phase-locked loop (SOGI-PLL). The resonant controller is tuned with the detected frequency by this harmonic detector. However, adding others stages to detect more harmonic components can lead to steady state error during the harmonic current detection process, due to nonideal filter characteristic of the SOGI-PLL structure. For this reason, this work proposes an improvement in the harmonic detector in order to compensate more than one harmonic component The strategy is applied in a three-phase system. Simulation results show the performance of the proposed control strategy, improving significantly the grid current quality.