Simplified multi-modular shunt active power filter system and its modelling

To meet the requirement of large capacity for harmonic suppression and reactive power compensation, modular shunt active power filter (SAPF) system is attractive for its high-reliability and flexibility. However, a unique physical address is needed for each module in traditional SAPFs. If a module fails, the faulted module should be substituted by another one with the same physical address. Therefore it is hard to realise modularisation, and the cost of the system is high. In addition, in such a system, a single SAPF generally adopts the topology with LCL filter and are coupled because of grid impedance. Generally, this coupling is not taken into account when designing the control laws. In consequence, depending on the number of paralleled SAPFs and the grid impedance, the paralleled SAPFs do not behave as expected. In this study, a simplified N + 1 redundant SAPF system and its control strategy are presented. The SAPFs are modelled as a multivariable system. The analysis carried out enables to obtain an equivalent SAPF that describes the totality of paralleled SAPFs. The coupling effect is described and the control law design of paralleled SAPFs with LCL filters is clarified. The validity of the simplified N + 1 SAPF system and the efficiency of the control strategies are demonstrated by prototype experiments.