Abstract
Energy storage systems play a key role in the rise of distributed power generation systems, hence there is great interest in extending their lifetimes, which are directly related to DC current ripple. One of the ripple sources is the low-frequency active power fluctuations under unbalanced and distorted grid voltage conditions. Therefore, this paper addresses a multifrequency control strategy where the harmonic reference currents are calculated to reduce harmonic active power oscillations. The stationary reference frame (StRF) approach taken here improves the precision and computational time of the current reference calculation method. Additionally, in order to ensure safe converter operation when a multifrequency reference current is provided, a computational efficient peak current saturator is applied while avoiding signal distortion every time step. If the injected current harmonic distortion is to be minimized, which is a feature included in this work, the peak current saturator is a necessary requirement. Active power ripple is reduced even with frequency variations in the grid voltage using a well-known frequency-adaptive scheme. The simulation and experimental results prove the optimized performance for the control objective: power ripple reduction with minimum current harmonic distortion.
Highlights
Nowadays, distributed energy resources (DER) are leading the change in power generation as a result of the interest in renewable energy systems (RES) [1]
The operation as STATCOM let us clearly study the control objective because high current can be achieved and the instantaneous active power exchange is mainly related to active power oscillations
The presented simulation has been set up for 5 Current reference generator (CRG) situations, where the calculated current reference is beyond the specified saturation value (ISAT = 50A) in order to notice the effectiveness of the Maximum Peak Current Saturator (MPCS) in the first four cases, and what happens when it is not employed
Summary
Nowadays, distributed energy resources (DER) are leading the change in power generation as a result of the interest in renewable energy systems (RES) [1]. Previous publications such as References [17,18,19] claimed the elimination of both active and reactive power oscillations, simultaneously This approach in three-wire systems leads to the injection of zero-sequence currents. The multifrequency current reference calculator purpose, just taking into account positive and negative sequences, has been partly fulfilled for DER applications [5] as well as DFIG ones [10,22] Both proposals are defined in synchronous reference frames (SRF), coordinate transformations are required. In Reference [27], which is a STATCOM application, the peak current is limited by defining the maximum reactive power that varies with the voltage characteristics and a control gain.
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